Method and device for accelerating data processing of double connection in next generation mobile communication system

ABSTRACT

Disclose are: a communication technique for merging, with IoT technology, a 5G communication system for supporting a data transmission rate higher than that of a 4G system; and a system therefor. The present disclosure can be applied to an intelligent service (for example, smart home, smart building, smart city, smart car or connected car, health care, digital education, retail, security and safety-related services, and the like) on the basis of a 5G communication technology and an IoT-related technology. One embodiment of the present invention relates to a method and a device for accelerating data processing of a double connection in a next generation mobile communication system.

TECHNICAL FIELD

The disclosure relates to a method and apparatus for accelerating dualconnectivity data processing in a next generation mobile communicationsystem.

BACKGROUND ART

To meet the increased demand for wireless data traffic since thedeployment of 4G communication systems, efforts have been made todevelop an improved 5G or pre-5G communication system. Therefore, the 5Gor pre-5G communication system is also called a “Beyond 4G Network” or a“Post LTE System”.

Implementation of the 5G communication system in higher frequency(mmWave) bands, e.g., 60 GHz bands, is being considered in order toaccomplish higher data rates. To decrease propagation loss of radiowaves and increase the transmission distance, beamforming, massivemultiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO),array antenna, analog beam forming, and large scale antenna techniquesare being discussed for the 5G communication system. In addition, in the5G communication system, there are developments underway for systemnetwork improvement based on advanced small cells, cloud Radio AccessNetworks (RANs), ultra-dense networks, device-to-device (D2D)communication, wireless backhaul, moving network, cooperativecommunication, Coordinated Multi-Points (CoMP), reception-endinterference cancellation, and the like.

In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and slidingwindow superposition coding (SWSC) as advanced coding modulation (ACM)and filter bank multi carrier (FBMC), non-orthogonal multiple access(NOMA), and sparse code multiple access (SCMA) as advanced accesstechnology have been developed.

The Internet, which is a human centered connectivity network wherehumans generate and consume information, is now evolving into theInternet of Things (IoT) where distributed entities, such as things,exchange and process information without human intervention. TheInternet of Everything (IoE), which is a combination of IoT technologyand Big Data processing technology through connection with a cloudserver, has emerged. As technology elements, such as “sensingtechnology”, “wired/wireless communication and network infrastructure”,“service interface technology”, and “security technology” have beendemanded for IoT implementation, recently there has been research into asensor network, Machine-to-Machine (M2M) communication, Machine TypeCommunication (MTC), and so forth.

Such an IoT environment may provide intelligent Internet technologyservices that create new values for human life by collecting andanalyzing data generated among connected things. The IoT may be appliedto a variety of fields including smart home, smart building, smart city,smart car or connected car, smart grid, health care, smart appliances,and advanced medical services through convergence and combinationbetween existing Information Technology (IT) and various industrialapplications.

In line with these developments, various attempts have been made toapply the 5G communication system to IoT networks. For example,technologies such as a sensor network, Machine Type Communication (MTC),and Machine-to-Machine (M2M) communication may be implemented bybeamforming, MIMO, and array antennas. Application of a cloud RadioAccess Network (RAN) as the above-described Big Data processingtechnology may also be considered to be an example of convergencebetween the 5G technology and the IoT technology.

DISCLOSURE OF INVENTION Technical Problem

In a next generation mobile communication system, data may bepre-processed before being allocated transmission resources for dataprocessing acceleration. However, it is difficult to pre-process data inthe case of using a split bearer for dual connectivity. In the dualconnectivity using a split bearer, data pre-processing may be performedafter a packet data convergence protocol (PDCP) entity determines one oftwo radio link control (RLC) entities to which the data packets are tobe sent.

That is, the PDCP entity does not send any data packets to either of thetwo associated RLC entities before transmission resources are allocatedto respective connections in dual connectivity and this means that thereis no data preprocessing.

Solution to Problem

According to an embodiment of the disclosure, a method of a first basestation in a wireless communication system includes transmitting anaddition request message to a second base station to request for addingthe second base station based on a determination for handover of aterminal being served by the first base station, transmitting to thesecond base station a handover request message including information forswitching from a Primary Cell (PCell) of the first base station to aPrimary Secondary Cell (PSCell) and from the PSCell of the second basestation to the PCell for the terminal based on a predetermined conditionbeing satisfied, and releasing a connection between the first basestation and the terminal based on receiving a release request messagefrom the second base station.

According to an embodiment of the disclosure, a method of a terminal ina wireless communication system includes receiving, from a first basestation to which the terminal is wirelessly connected, a radio resourcecontrol (RRC) reconfiguration message including configurationinformation related to a split bearer between the first base station anda second base station added by the first base station, receiving, fromthe first base station, a handover command message including informationindicative of switching from a Primary Cell (PCell) of the first basestation to a Primary Secondary Cell (PSCell) and from the PSCell of thesecond base station to the PCell, and releasing a wireless connection tothe first base station.

According to an embodiment of the disclosure, a first base station in awireless communication system includes a transceiver configured totransmit an addition request message to a second base station to requestfor adding the second base station based on a determination for handoverof a terminal being served by the first base station and a controllerconfigured to control the transceiver to transmit, to the second basestation, a handover request message including information for switchingfrom a Primary Cell (PCell) of the first base station to a PrimarySecondary Cell (PSCell) and from the PSCell of the second base stationto the PCell for the terminal based on a predetermined condition beingsatisfied and release a connection between the first base station andthe terminal based on receiving a release request message from thesecond base station.

According to an embodiment of the disclosure, a terminal in a wirelesscommunication system includes a transceiver configured to receive, froma first base station to which the terminal is wirelessly connected, aradio resource control (RRC) reconfiguration message includingconfiguration information related to a split bearer between the firstbase station and a second base station added by the first base stationand a controller configured to control the transceiver to receive, fromthe first base station, a handover command message including informationindicative of switching from a Primary Cell (PCell) of the first basestation to a Primary Secondary Cell (PSCell) and from the PSCell of thesecond base station to the PCell and release a wireless connection tothe first base station.

Advantageous Effects of Invention

According to an embodiment, the disclosure is advantageous in terms ofminimizing a data communication cut-off state occurring during ahandover.

According to another embodiment, the disclosure is advantageous in termsof protecting against erroneous operations of a terminal by restrictinga validity of configuration information received from a base stationonly to the corresponding base station and, when the terminal moves to anew base station, allowing the new base station to have all necessaryconfiguration information.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a diagram illustrating an architecture of an LTE system;

FIG. 1B is a diagram illustrating a protocol stack in an LTE system;

FIG. 1C is a diagram illustrating a next generation mobile communicationsystem architecture proposed in the disclosure;

FIG. 1D is a diagram illustrating a protocol stack in a next generationmobile communication system proposed in the disclosure;

FIG. 1E is a signal flow diagram illustrating a procedure forconfiguring layer-specific entities at a UE in a next generation mobilecommunication system according to an embodiment of the disclosure;

FIG. 1F is a diagram for explaining scenarios for a UE to receive aservice via an LTE eNB or an NR gNB in a next generation mobilecommunication system according to an embodiment of the disclosure;

FIG. 1G is a diagram illustrating a method for preprocessing dataaccording to an embodiment of the disclosure;

FIG. 1H is a diagram for explaining a data preprocessing method in adual connectivity split bearer environment in a next generation mobilecommunication system according to an embodiment of the disclosure;

FIGS. 1IA to FIG. 1IC are flowcharts illustrating operations of PDCP,RLC, and MAC entities in a UE;

FIG. 1J shows operations of a PDCP entity for sending data packets to afirst RLC entity and a second RLC entity according to a predeterminedsplit ratio, in embodiments 1-1 and 1-2 that embody methods forpreprocessing data in a dual connectivity split bearer environment in anext generation mobile communication system, according to embodiment1-3-1 of the disclosure;

FIG. 1K is diagrams illustrating operations of a PDCP entity for sendingdata packets to a first RLC entity and a second RLC entity according toa predetermined split ratio, in embodiments 1-1 and 1-2 that embodymethods for preprocessing data in a dual connectivity split bearerenvironment in a next generation mobile communication system, accordingto embodiment 1-3-2 of the disclosure;

FIG. 1L is a diagram illustrating operations of a PDCP entity forsending data packets to a first RLC entity and a second RLC entityaccording to a predetermined split ratio, in embodiments 1-1 and 1-2that embody methods for preprocessing data in a dual connectivity splitbearer environment in a next generation mobile communication system,according to embodiment 1-3-3 of the disclosure;

FIG. 1M is a diagram illustrating operations of a PDCP entity forsending data packets to a first RLC entity and a second RLC entityaccording to a predetermined split ratio, in embodiments 1-1 and 1-2that embody methods for preprocessing data in a dual connectivity splitbearer environment in a next generation mobile communication system,according to embodiment 1-3-4 of the disclosure;

FIG. 1N is a diagram illustrating operations of a PDCP entity forsending data packets to a first RLC entity and a second RLC entityaccording to a predetermined split ratio, in embodiments 1-1 and 1-2that embody methods for preprocessing data in a dual connectivity splitbearer environment in a next generation mobile communication system,according to embodiment 1-3-5 of the disclosure;

FIG. 1O is a diagram illustrating operations of a PDCP entity forsending data packets to a first RLC entity and a second RLC entityaccording to a predetermined split ratio, in embodiments 1-1 and 1-2that embody methods for preprocessing data in a dual connectivity splitbearer environment in a next generation mobile communication system,according to embodiment 1-3-6 of the disclosure;

FIG. 1P is a diagram illustrating operations of a PDCP entity forsending data packets to a first RLC entity and a second RLC entityaccording to a predetermined split ratio, in embodiments 1-1 and 1-2that embody methods for preprocessing data in a dual connectivity splitbearer environment in a next generation mobile communication system,according to embodiment 1-3-7 of the disclosure;

FIG. 1Q is a diagram illustrating operations of a PDCP entity forsending data packets to a first RLC entity and a second RLC entityaccording to a predetermined split ratio, in embodiments 1-1 and 1-2that embody methods for preprocessing data in a dual connectivity splitbearer environment in a next generation mobile communication system,according to embodiment 1-3-8 of the disclosure;

FIG. 1R is a block diagram illustrating a configuration of a UEaccording to an embodiment of the disclosure;

FIG. 1S is a block diagram illustrating a TRP in a wirelesscommunication system according to an embodiment of the disclosure;

FIG. 2A is a diagram for conceptually explaining the inter-systemhandover by applying a dual-registered technique in a next generationmobile communication system;

FIG. 2B is a signal flow diagram illustrating signal flows in a casewhere a UE moves from a service area of a next generation mobilecommunication system to a service area of a legacy stem system accordingto an embodiment of the disclosure;

FIG. 2C is a signal flow diagram illustrating signal flows in a casewhere a UE moves from a service area of a next generation mobilecommunication system to a service area of a legacy LTE system accordingto an embodiment of the disclosure;

FIG. 2D is a flowchart illustrating a procedure for a network todetermine initialization of a dual-registered operation;

FIG. 2E is a diagram for explaining scenarios where a dual-registered UEis in an idle mode in two respective systems;

FIG. 2F is a signal flow diagram for explaining a first solutionaccording to an embodiment of the disclosure;

FIG. 2G is a flowchart illustrating operations of a UE in the firstsolution according to an embodiment of the disclosure;

FIG. 2H is a flowchart for explaining operations of an NG Core or an MMEin the first solution of the disclosure;

FIG. 2I is a flowchart for explaining operations of a Common IP Anchorin the first solution of the disclosure;

FIG. 2J is a signal flow diagram for explaining a second solutionaccording to an embodiment of the disclosure;

FIG. 2K is a signal flow diagram for explaining a power saving mode(PSM);

FIG. 2L is a flowchart for explaining operations of a UE in the secondsolution of an embodiment of the disclosure;

FIG. 2M is a flowchart for explaining operations of an NG Core or an MMEin the second solution of the disclosure;

FIG. 2N is a flowchart illustrating operations of a Common IP Anchor inthe second solution of the disclosure;

FIG. 2O is a block diagram illustrating a configuration of a UEaccording to an embodiment of the disclosure;

FIG. 2P is a block diagram illustrating a configuration of a basestation according to an embodiment of the disclosure;

FIG. 3A is a diagram illustrating an architecture of a legacy LTEsystem;

FIG. 3B is a diagram illustrating a protocol stack in an LTE system;

FIG. 3C is a schematic diagram illustrating a dual-connectivityoperation in a legacy LTE system;

FIG. 3D is a diagram illustrating a next generation mobile communicationsystem architecture to which the disclosure is applied;

FIG. 3E is a signal flow diagram illustrating a handover procedure in anLTE system for reference to explain the disclosure;

FIGS. 3FA and 3FB are schematic diagrams for explaining a DC- and RLCsplit bearer-based inter-gNB handover operation and a protocol structureaccording to embodiment 3-1 of the disclosure;

FIGS. 3GA and 3GB are signal flow diagrams illustrating a DC- and RLCsplit bearer-based handover procedure according to embodiment 3-1 of thedisclosure;

FIGS. 3HA and 3HB are schematic diagrams for explaining a DC- and RLCsplit bearer-based inter-gNB handover operation and a protocol structureaccording to embodiment 3-1 of the disclosure;

FIGS. 1A and 3IB are signal flow diagrams illustrating a DC- and RLCsplit bearer-based handover procedure according to embodiment 3-2 of thedisclosure;

FIG. 3J is a flowchart illustrating a DC- and RLC split bearer-basedType 2 handover procedure of a UE according to an embodiment of thedisclosure;

FIG. 3k is a block diagram illustrating a configuration of a UEaccording to an embodiment of the disclosure; and

FIG. 3L is a block diagram illustrating a configuration of an NR gNBaccording to an embodiment of the disclosure.

MODE FOR THE INVENTION

The operation principle of the disclosure is described in detail withreference to the accompanying drawings. Detailed descriptions ofwell-known functions and structures incorporated herein may be omittedto avoid obscuring the subject matter of the disclosure. Further, thefollowing terms are defined in consideration of the functionality in thedisclosure, and they may vary according to the intention of a user or anoperator, usage, etc. Therefore, the definition should be made on thebasis of the overall content of the present specification.

Detailed descriptions of well-known functions and structuresincorporated herein may be omitted to avoid obscuring the subject matterof the disclosure. Exemplary embodiments of the disclosure are describedhereinafter in detail with reference to the accompanying drawings.

The terms used, in the following description, for indicating accessnodes, network entities, messages, interfaces between network entities,and diverse identity informations are provided for convenience ofexplanation. Accordingly, the terms used in the following descriptionare not limited to specific meanings, and they may be replaced by otherterms equivalent in technical meaning

In the following description, the terms and definitions given in the 3rdGeneration Partnership Project Long Term Evolution (3GPP LTE) standardare used. However, the disclosure is not limited by the terms anddefinitions, and it can be applied to other standard communicationsystems.

First Embodiment

FIG. 1A is a diagram illustrating architecture of an LTE system.

In reference to FIG. 1A, the radio communication system includes evolvedNode Bs (eNBs) 1 a-05, 1 a-10, 1 a-15, and 1 a-20; a Mobility ManagementEntity (MME) 1 a-25; and a Serving Gateway (S-GW) 1 a-30. The UserEquipment (UE or terminal) 1 a-35 connects to an external network viathe eNBs 1 a-05, 1 a-10, 1 a-15, and 1 a-20 and the S-GW 1 a-30.

In FIG. 1A, the eNBs 1 a-05, 1 a-10, 1 a-15, and 1 a-20 correspond tolegacy node Bs of UMTS. The UE 135 connects to one of the eNBs via aradio channel, and the eNB has more complex functions than the legacynode B. In the LTE system where all user traffic including real timeservices such as Voice over IP (VoIP) is served through shared channels,there is a need of an entity for collecting UE-specific statusinformation (such as buffer status, power headroom status, and channelstatus) and scheduling the UEs based on the collected information, andthe eNBs 1 a-05, 1 a-10, 1 a-15, and 1 a-20 take charge of suchfunctions. Typically, one eNB hosts multiple cells. For example, the LTEsystem adopts Orthogonal Frequency Division Multiplexing (OFDM) as aradio access technology to secure a data rate of up to 100 Mbps in abandwidth of 20 MHz.

The LTE system also adopts Adaptive Modulation and Coding (AMC) todetermine the modulation scheme and channel coding rate in adaptation tothe channel condition of the UE. The S-GW 1 a-30 handles data bearerfunctions to establish and release data bearer under the control of theMME 1 a-25. The MME 1 a-25 handles various control functions for the UEas well as the mobile management function and has connections with theeNBs.

FIG. 1B is a diagram illustrating a protocol stack in an LTE system.

In reference to FIG. 1B, the protocol stack of the interface between theUE and the eNB in the LTE system includes a packet data convergencecontrol (PDCP) layer denoted by reference numbers 1 b-05 and 1 b-40,radio link control (RLC) layer denoted by reference numbers 1 b-10 and 1b-35, and a medium access control (MAC) layer denoted by referencenumbers 1 b-15 and 1 b-30. The PDCP layer denoted by reference numbers 1b-05 and 1 b-40 takes charge of compressing/decompressing an IP header.The main functions of the PDCP layer can be summarized as follows.

-   -   Header compression and decompression: ROHC only    -   Transfer of user data    -   In-sequence delivery of upper layer PDUs at PDCP        re-establishment procedure for RLC AM    -   Reordering for split bearers in DC (only support for RLC AM):        PDCP PDU routing for transmission and PDCP PDU reordering for        reception    -   Duplicate detection of lower layer SDUs at PDCP re-establishment        procedure for RLC AM    -   Retransmission of PDCP SDUs at handover and, for split bearers        in DC, of PDCP PDUs at PDCP data-recovery procedure, for RLC AM    -   Ciphering and deciphering    -   Timer-based SDU discard in uplink.

The RLC layer designated by reference number 1 b-10 and 1 b-35 takescharge of reformatting PDCP PDUs in order to fit them into a size forARQ operation. The main functions of the RLC layer can be summarized asfollows.

-   -   Transfer of upper layer PDUs    -   Error Correction through ARQ (only for AM data transfer)    -   Concatenation, segmentation, and reassembly of RLC SDUs (only        for UM and AM data transfer)    -   Re-segmentation of RLC data PDUs (only for AM data transfer)    -   Reordering of RLC data PDUs (only for UM and AM data transfer)    -   Duplicate detection (only for UM and AM data transfer)    -   Protocol error detection (only for AM data transfer)    -   RLC SDU discard (only for UM and AM data transfer)    -   RLC re-establishment

The MAC layer denoted by reference numbers 1 b-15 and 1 b-30 allows forconnection of multiple RLC entities established for one UE and takescharge of multiplexing RLC PDUs from the RLC layer into a MAC PDU anddemultiplexing a MAC PDU into RLC PDUs. The main functions of the MAClayer can be summarized as follows.

-   -   Mapping between logical channels and transport channels    -   Multiplexing/demultiplexing of MAC SDUs belonging to one or        different logical channels into/from transport blocks (TB)        delivered to/from the physical layer on transport channels    -   Scheduling information reporting    -   Error correction through HARQ    -   Priority handling between logical channels of one UE    -   Priority handling between UEs by means of dynamic scheduling    -   MBMS service identification    -   Transport format selection    -   Padding

The physical layer denoted by reference numbers 1 b-20 and 1 b-25 takescharge of channel-coding and modulation on higher layer data to generateand transmit OFDM symbols over a radio channel, and demodulating andchannel-decoding on OFDM symbols received over the radio channel todeliver the decoded data to the higher layers.

FIG. 1C is a diagram illustrating a next generation mobile communicationsystem architecture proposed in the disclosure.

As shown in FIG. 1C, the next generation mobile communication systemincludes a radio access network with a next generation base station (NewRadio Node B (NR gNB) or NR base station) 1 c-10 and a new radio corenetwork (NR CN) 1 c-05. A new radio user equipment (NR UE or NRterminal) 1 c-15 connects to an external network via the NR gNB 1 c-10and the NR CN 1 c-05.

In FIG. 1C, the NR gNB 1 c-10 corresponds to an evolved Node B (eNB) ofthe legacy LTE. The NR gNB 1 c-10 to which the NR UE 1 c-15 connectsthrough a radio channel is capable of providing superior services incomparison with the legacy eNB. In the next generation mobilecommunication system where all user traffic is served through sharedchannels, it is necessary to schedule the NR UEs based on schedulinginformation such as buffer status, power headroom status, and channelstatus collected by the NR UEs, and the NR gNB 1 c-10 takes charge ofthis function.

Typically, one NR gNB operates multiple cells. In order to achieve adata rate higher than the peak data rate of legacy LTE systems, the nextgeneration mobile communication system may adopt a beamforming techniquealong with orthogonal frequency division multiplexing (OFDM) as a radioaccess technology.

The next generation mobile communication system may also adopt adaptivemodulation and coding (AMC) to determine the modulation scheme andchannel coding rate in adaptation to the channel condition of the NR UE.The NR CN 1 c-05 takes charge of mobility support, bearer setup, and QoSconfiguration. The NR CN 1 c-05 may take charge of an NR UE mobilitymanagement function, and a plurality of NR gNBs may connect to the NR CN1 c-05. The next generation mobile communication system may alsointeroperate with a legacy LTE system and, in this case, the NR CN 1c-05 connects to an MME 1 c-25 through a network interface. The MME 1c-25 communicates with at least one eNB 1 c-30 as a legacy base station.

FIG. 1D is a diagram illustrating a protocol stack in a next generationmobile communication system proposed in the disclosure.

In reference to FIG. 1D, the protocol stack of the interface between anNR UE and an NR gNB in a next generation mobile communication systemincludes a NR PDCP layer denoted by reference numbers 1 d-05 and 1 d-40,an NR RLC layer denoted by reference numbers 1 d-10 and 1 d-35, and anNR MAC layer denoted by reference numbers 1 d-15 and 1 d-30. The mainfunctions of the NR PDCP layer denoted by reference numbers 1 d-05 and 1d-40 may include some of the following functions.

-   -   Header compression and decompression: ROHC only    -   Transfer of user data    -   In-sequence delivery of upper layer PDUs    -   PDCP PDU reordering for reception    -   Duplicate detection of lower layer SDUs    -   Retransmission of PDCP SDUs    -   Ciphering and deciphering    -   Timer-based SDU discard in uplink.

The PDCP PDU reordering function of an NR PDCP entity is to reorder thePDCP PDUs delivered from a lower layer based on the PDCP sequence number(PDCP SN) and may include delivering the reordered data to an upperlayer, recording the missing PDCP PDUs among the reordered PDCP PDUs,transmitting a status report indicating the missing PDCP PDUs to thesender, and requesting for retransmission of the missing PDCP PDUs.

The main functions of the NR RLC layer denoted by reference numbers 1d-10 and 1 d-35 may include some of the following functions.

-   -   Transfer of upper layer PDUs    -   In-sequence delivery of upper layer PDUs    -   Out-of-sequence delivery of upper layer PDUs    -   Error Correction through ARQ    -   Concatenation, segmentation, and reassembly of RLC SDUs    -   Re-segmentation of RLC data PDUs    -   Reordering of RLC data PDUs    -   Duplicate detection    -   Protocol error detection    -   RLC SDU discard    -   RLC re-establishment

The in-sequence delivery function of an NR RLC entity is to deliver theRLC SDUs received from the lower layer to the upper layer and mayinclude reassembling, when multiple segmented RLC SDUs constituting anoriginal RLC SDU are received, the RLC SDUs and delivering thereassembled RLC SDU to the upper layer; reordering the received RLC PDUsbased on the RLC sequence number(SN) or PDCP SN; recording the missingRLC PDUs among the reordered RLC PDUs; transmitting a status reportindicating the missing RLC PDUs to the sender; requesting forretransmission of the missing RLC PDUs; and delivering, when there is amissing RLC PDU, the RLC PDUs before the missing RLC PDU in sequence,delivering, if a predetermined timer expires even when there is amissing RLC SDU, all RLC SDUs received before the start of the timer tothe upper layer in sequence, or delivering, if a predetermined timerexpires even when there is a missing RLC SDU, all RLC SDUs receiveduntil then to the upper layer in sequence. It may also be possible toprocess the RLC PDUs in the receiving sequence (in the order of arrivalregardless of sequence number) and deliver the RLC PDUs to the PDCPentity out of order (out-of-sequence delivery) and, if an RLC PDU istransmitted in the form of segments, to store the received segments, orwait until all segments constituting the RLC PDU are received andreassemble the segments into the original RLC PDU, which is delivered tothe PDCP entity.

The NR RLC layer may have no concatenation function and, in this case,the concatenation function may be performed in the NR MAC layer orreplaced by the multiplexing function of the NR MAC layer.

The out-of-sequence delivery function of an NR RLC entity is to deliverthe RLC SDUs received from the lower layer to the upper layer out oforder and may include reassembling, when multiple segmented RLC SDUsconstituting an original RLC SDU are received, the segmented RLC SDUs,delivering the reassembled RLC SDUs to the upper layer, arranging thereceived RLC PDUs based on the RLC SN or PDCP SN, and recording the SNof the missing RLC PDUs.

In the NR MAC layer denoted by reference numbers 1 d-15 and 1 d-30, anNR MAC entity may be connected to multiple NR RLC entities, and the mainfunctions of the NR MAC entity may include some of the followingfunctions.

-   -   Mapping between logical channels and transport channels    -   Multiplexing/demultiplexing of MAC SDUs    -   Scheduling information reporting    -   Error correction through HARQ    -   Priority handling between logical channels of one UE    -   Priority handling between UEs by means of dynamic scheduling    -   MBMS service identification    -   Transport format selection    -   Padding

The NR PHY layer denoted by reference numbers 1 d-20 and 1 d-25 takescharge of channel-coding and modulation on upper layer data to generateand transmit OFDM symbols over a radio channel and demodulating andchannel-decoding on OFDM symbols received over the radio channel todeliver the decoded data to the upper layers.

FIG. 1E is a signal flow diagram illustrating a procedure forconfiguring layer-specific entities at a UE in a next generation mobilecommunication system according to an embodiment of the disclosure.

FIG. 1E shows a procedure for a UE to establish a connection with anetwork for data communication and configure layer-specific entitiesaccording to an embodiment of the disclosure.

If data to be transmitted is generated at the UE 1 d-01 in an idle mode(hereinafter, referred to as idle mode UE), the UE may initiate a radioresource control (RRC) connection establishment procedure with an LTEeNB or NR gNB 1 d-02. The UE acquires uplink synchronization with theeNB or gNB through a random access procedure and transmits an RRCConnection Request (RRCConnectionRequest) message to the eNB gNB at step1 d-05. This message includes an identifier of the UE and a reason forestablishing the connection.

The eNB or gNB transmits an RRC connection setup (RRCConnectionSetup)message to the UE at step 1 d-10. This message may include RRCconnection configuration information and layer-specific configurationinformation. That is, this message may include PHY or NR PHY entityconfiguration information, MAC or NR MAC entity configurationinformation, RLC or NR RLC entity configuration information, PDCP or NRPDCP entity configuration information, and information for configuringspecific functions among the functions supported by the layer-specificentities (layer-specific functions described with reference to FIG. 1Bor FIG. 1D). This message may also include a predetermined bearer splitratio value to be applied at the PDCP entity or information on whetherto configure RLC entities, threshold 1, or threshold 2.

The RRC connection is also referred to as a signaling radio bearer (SRB)and used for communicating RRC messages as control messages beingexchanged between the UE and the eNB or gNB. After establishing the RRCconnection, the UE transmits an RRC Connection Setup Complete(RRCConnectionSetupComplete) message to the eNB or gNB at step 1 d-15.

The eNB or gNB transmits an RRC Connection Reconfiguration(RRCConnectionReconfiguration) message to the UE at step 1 d-20 forsetting up a data radio bearer (DRB). This message may includelayer-specific configuration information. That is, this message mayinclude PHY or NR PHY entity configuration information, MAC or NR MACentity configuration information, RLC or NR RLC entity configurationinformation, PDCP or NR PDCP entity configuration information, andinformation for configuring specific functions among the functionssupported by the layer-specific entities (layer-specific functionsdescribed with reference to FIG. 1B or FIG. 1D). This message may alsoinclude a predetermined bearer split ratio value to be applied at thePDCP entity or information on whether to configure RLC entities,threshold 1, or threshold 2.

This message may also include configuration information on DRB forprocessing user data, and the UE establishes a DRB and configureslayer-specific functions based on the above information and transmits anRRC Connection Reconfiguration Complete(RRCConnectionReconfigurationComplete) message to the eNB or gNB at step1 d-25.

Once the above procedure is completed, the UE and the eNB or gNBcommunicate data at step 1 d-30. If necessary, the eNB or gNB maytransmit the RRCConnectionReconfiguration message to the UE at step 1d-35, during the data communication, for reconfiguring thelayer-specific configurations of the UE. That is, this message mayinclude PHY or NR PHY entity configuration information, MAC or NR MACentity configuration information, RLC or NR RLC entity configurationinformation, PDCP or NR PDCP entity configuration information, andinformation for configuring specific functions among the functionssupported by the layer-specific entities (layer-specific functionsdescribed with reference to FIG. 1B or FIG. 1D).

This message may also include a predetermined bearer split ratio valueto be applied at the PDCP entity or information on whether to configureRLC entities, threshold 1, or threshold 2. This message may also includeconfiguration information on interworking between the LTE eNB (or NRgNB) and an NR gNB). The configuration information on interworkingbetween the LTE eNB and the NR gNB may include information indicatingtype 3C or type 1A and layer-specific entity information per type.

Once the layer-specific entity configuration is completed based on theabove message, the UE transmits an RRCConnectionReconfigurationCompletemessage to the eNB or gNB at step 1 d-40.

FIG. 1F is a diagram for explaining scenarios for a UE to receive aservice via an LTE eNB or an NR gNB in a next generation mobilecommunication system according to an embodiment of the disclosure.

In FIG. 1F, reference number 1 f-01 denotes a scenario of type 3Cinterworking between two LTE eNBs of which one is associated with amaster cell group (MCG) and the other is associated with a secondarycell group (SCG), reference number 1 f-02 denotes a scenario of type 3Cinterworking between an LTE eNB associated with an MCG and an NR gNBassociated with an SCG, reference number 1 f-03 denotes a scenario oftype 3C interworking between an LTE eNB associated with an SCG and an NRgNB associated with an MCG, and reference number 1 f-04 denotes ascenario of type 3C interworking between two NR gNBs of which one isassociated with an MCG and the other is associated with an SCG.

FIG. 1G is a diagram illustrating a method for preprocessing dataaccording to an embodiment of the disclosure.

In the scenarios as denoted by reference numbers 1 f-01, 1 f-02, 1 f-03,and 1 f-04 in FIG. 1F, a data packet 1 f-05 from a higher layer in auser plane may be preprocessed at an NR gNB or a UE of the nextgeneration mobile communication system. Preprocessing the data meanspreprocessing an IP packet to generate a PDCP PDU 1 f-10 of the PDCPlayer, an RLC PDU 1 f-15 of the RLC layer, or a MAC SDU 1 f-20 of theMAC layer along with a MAC sub-header.

FIG. 1H is a diagram for explaining a data preprocessing method in adual connectivity split bearer environment in a next generation mobilecommunication system according to an embodiment of the disclosure.

Hereinafter, a description is made of the data preprocessing in the dualconnectivity split bearer environment in a next generation mobilecommunication system according to embodiment 1-1 of the disclosure. Thesplit bearer is a DRB that is capable of increasing a data rate byallowing a PDCP entity 1 h-05 to send data packets in a distributedmanner to two RLC entities 1 h-10 and 1 h-15 that transmit data throughdifferent cells.

According to an embodiment of the disclosure, the dual connectivityenvironment may include the scenarios 1 f-01, 1 f-02, 1 f-03, and 1 f-04of FIG. 1F of which each may be applicable to a situation of using adual connectivity downlink (DL) split bearer at a base station and asituation of using a dual connectivity uplink (UL) split bearer at a UE.The disclosure may be applied to the above scenarios.

In the case of using a split bearer in a dual connectivity environment,the PDCP entity 1 h-05 may process data packets (IP packets or PDCPSDUs) into PDCP PDUs and send the PDCP PDUs to a first RLC entity 1 h-10and a second RLC entity 1 h-15 according to a predetermined ratio. Thepredetermined ratio may be determined by a network (or base station ofan MCG or an SCG) and transmitted to a UE via an RRC message (or a newlydefined MAC CE or a newly defined PDCP control PDU) (in downlink, thePDCP entity of the MCG may immediately acquire information on thepredetermined ratio from the network).

For example, the base station may transmit the predetermined ratio andinformation on whether the first and second RLC entities are establishedto the UE via the RRCConnectionSetup message at step 1 e-10 or theRRCConnectionReconfiguration message at steps 1 e-20 and 1 e-35 in FIG.1E. If the predetermined ratio is configured and the first and secondRLC entities are established, the PDCP entity 1 h-05 sends data to thefirst and second RLC entities 1 h-10 and 1 h-15 according to the ratio.It may also be possible to tag the data packets with MCG or SCGaccording to the ratio and make a record thereof Here, it may bepossible to interpret that the MCG and SCG correspond respectively tothe first and second RLC entities.

For example, if the predetermined ratio is set to 2:1, two data packetsare sent to the first RLC entity while one data packet is sent to thesecond RLC entity. The PDCP entity may repeat the above procedure.

The data packets 1 g-10 sent to the first and second RLC entities may bepreprocessed into a MAC SDU 1 g-20 along with a MAC sub-header asdescribed with reference to FIG. 1G. The data preprocessing process maybe continuously performed when the total size of the preprocessed datapackets is equal to or less than a predetermined threshold 1.

If the total size of the preprocessed data packets is equal to orgreater than the predetermined threshold 1, the preprocessing processmay be stopped. If transmission resources are allocated and datatransmission is completed such that the total size of the preprocesseddata packets become less than the predetermined threshold 1, thepreprocessing process may be resumed.

If transmission resources are allocated to the MCG or SCG for datatransmission, the MCG or SCG generates MAC PDUs fit in size to thetransmission resources with the preprocessed data packets and, if thesize of the transmission resources is less than the size of thepreprocessed data packets, it may segment the last MAC SDU, update theMAC sub-header correspondingly, and generate a MAC PDU.

Threshold 1 may be determined by a network (or base station of the MCGor SCG) and transmitted to a UE via an RRC message (or a newly definedMAC CE or a newly defined PDCP control PDU) (in downlink, the PDCPentity of the MCG may immediately acquire information on threshold 1from the network).

For example, the base station may transmit threshold 1 to the UE via theRRCConnectionSetup message at step 1 e-10 or theRRCConnectionReconfiguration message at steps 1 e-20 and 1 e-35 of FIG.1E. Depending on UE capability, the UE may determine the valueautonomously. That is, the UE may set threshold 1 to a valuecorresponding to a size of the largest transport block (TB) or a TB fora highest data rate (highest rate TB). The UE may also set threshold 1to a value obtained by multiplying the highest rate by a round trip time(RTT). Threshold 1 may be defined by a number of data packets or bytesindicative of data size.

In embodiment 1-1 of the disclosure, the PDCP entity 1 h-05, the RLCentities 1 h-10 and 1 h-15, and the MAC entities 1 h-20 and 1 h-25operate as follows.

If a first condition is fulfilled, the PDCP entity 1 h-05 follows afirst method; if a second condition and a third condition are fulfilled,the PDCP entity 1 h-05 follows a second method; if the second conditionand a fourth condition are fulfilled, the PDCP entity 1 h-05 follows athird method.

The first condition is that the PDCP entity receives data packets from ahigher layer and one of the first and second RLC entities is configuredto process and send the data packets (whether the first RLC entityand/or the second RLC entity is configured may be determined by thenetwork (or a base station of the MCG or SCG) and notified to the UE viaan RRC message (or a newly defined MAC CE, a newly defined PDCP controlPDU, etc.) (in downlink, the PDCP entity of the MCG may directly acquireRLC entity configuration information from the network). For example, thebase station may notify the UE whether the first and second RLC entitiesare configured using the RRCConnectionSetup message at step 1 e-10 orthe RRCConnectionReconfiguration message at steps 1 e-20 and 1 e-35 ofFIG. 1E.).

The second condition is that the PDCP entity receives data packets fromthe higher layer and both the first and second RLC entities areconfigured to process and send the data packets (whether the first RLCentity and/or the second RLC entity is configured may be determined bythe network (or a base station of the MCG or SCG) and notified to the UEvia an RRC message (or a newly defined MAC CE, a newly defined PDCPcontrol PDU, etc.) (in downlink, the PDCP entity of the MCG may directlyacquire RLC entity configuration information from the network). Forexample, the base station may notify the UE whether the first and secondRLC entities are configured using the RRCConnectionSetup message at step1 e-10 or the RRCConnectionReconfiguration message at steps 1 e-20 and 1e-35 of FIG. 1E.).

The third condition is that a ratio is predetermined and a size ofpreprocessed data packets is equal to or less than threshold 1.

The fourth condition is that a ratio is predetermined and a size ofpreprocessed data packets is greater than threshold 1.

In the first method, the PDCP entity processes the data packets from thehigher layer into PDCP PDUs and sends them to one of the first andsecond RLC entities that is configured to process and send data packets.

In the second method, the PDCP entity processes the data packets fromthe higher layer into PDCP PDUs and sends the PDCP PDUs to the first andsecond RLC entities according to a predetermined ratio.

In the third method, the PDCP entity holds the PDCP PDUs generated byprocessing the data packets from the higher layer without sending themto the first and second RLC entities and waits until the third conditionis fulfilled.

The RLC entities 1 h-10 and 1 h-15 follow the first method for the casewhere the first condition is fulfilled and the second method for thecase where the second condition is fulfilled.

The first condition is the case where the RLC entities are LTE RLCentities or eLTE RLC entities (the eLTE RLC entities are evolved LTE RLCentities updated with new or improved functions).

The second condition is the case where the RLC entities are NR RLCentities (NR RLC entities of the next generation mobile communicationsystem may be characterized by including the functions described withreference to FIG. 1D with the exception of the concatenation function.

In the first method, the RLC entities store the PDCP PDUs received fromthe PDCP entity, waiting until transmission resources are allocated,generates, if transmission resources are allocated, RLC PDUs byconcatenating the PDCP PDUs to be fit in size for the transmissionresources and adding RLC headers, and send the RLC PDUs to thecorresponding MAC entities.

In the second method, the RLC entities generate RLC PDUs with RLCheaders for data preprocessing on the PDCP PDUs received from the PDCPentity as described with reference to FIG. 1G regardless of transmissionresources allocation and send the RLC PDUs to the corresponding MACentities, the MAC entities generating MAC sub-headers and MAC SDUs tocomplete the data preprocessing.

The MAC entities 1 h-20 and 1 h-25 follow the first method for the casewhere the first condition is fulfilled and the second method for thecase where the second condition is fulfilled.

The first condition is the case where the MAC entities are LTE MACentities or eLTE MAC entities (the eLTE MAC entities are evolved LTE MACentities updated with new or improved functions).

The second condition is the case where the MAC entities are NR MACentities (NR MAC entities of the next generation mobile communicationsystem may include the functions described with reference to FIG. 1D).

In the first method, the MAC entities stores the RLC PDUs received fromthe RLC entities, generate MAC PDUs with MAC sub-headers and MAC SDUs tobe fit in size for the transmission resources, and send the MAC PDUs tothe corresponding PHY entities.

In the second method, the MAC entities configure MAC sub-headers and MACSDUs by processing the RLC PDUs received from the RLC entities asdescribed with reference to FIG. 1G regardless of transmission resourcesallocation to complete the data preprocessing. If transmission resourcesare allocated, the MAC entities generate the MAC PDUs with the MACsub-headers and MAC SDUs to be fit in size for the transmissionresources and, if the size of the transmission resources is less thanrequired, segment the last MAC SDUs, update the MAC sub-header, and sendthe MAC PDUs to the corresponding PHY entities.

Threshold 1 may be set to a value corresponding to a size of the largesttransport block (TB) or a TB for a highest data rate (highest rate TB).Threshold 1 may also be set to a value obtained by multiplying thehighest rate by a round trip time (RTT). Threshold 1 may be defined by anumber of data packets or bytes indicative of data size.

Threshold 1 indicates a data amount necessary to be preprocessed at theUE. That is, if IP packets are continuously passed down to the PDCPlayer in the UE, preprocessing is performed by an amount set bythreshold 1 rather than in a continuous manner Threshold 1 may make itpossible to avoid unnecessary preprocessing at the UE.

Because threshold 1 is set to a value corresponding to a maximum ULtransmission resource amount (UL grant)/maximum data size (maximum TB)available for the UE, the UE may be able achieve a preprocessing gainwithout any loss. If the maximum UL transmission resource amount (ULgrant)/maximum data size (maximum TB) available for the UE increases byemploying a certain technology such as carrier aggregation andmulti-connectivity, threshold 1 may be reset to a value in adaptation tothe increase.

Threshold 1 may also be set per bearer or connected cell or basestation. Threshold 1 may also be used in a single connectivitysituation, i.e., a case where the UE connects to one base station fordata communication, as well as multi-connectivity situations.

Threshold 1 is configured by the network and broadcast in the systeminformation so as to be set as default to UEs; if threshold 1 isconfigured through the RRC Connection Setup, RRC Connection Resume, orRRC connection Reconfiguration procedure at steps 1 e-10, 1 e-20, or 1e-35 of FIG. 1E, the UE may apply the threshold value received via thisprocedure preferentially rather than the default value broadcast in thesystem information.

In embodiment 1-1 of the disclosure, the preprocessed data packets maybe canceled in a predetermined case. That is, it may be possible todiscard the preprocessed data packets and process original data packets(PDCP SDUs) stored in the PDCP entity according to embodiment 1-1. Thepredetermined case may be the case where the PDCP entity or the RLCentities are reset or reestablished or RLC entities are newlyestablished.

In embodiment 1-1 of the disclosure, if it is necessary for the UE toperform a buffer status report, i.e., if the UE has to make a bufferstatus report for a certain cell group, the UE may configure the bufferstatus report by summing the total size of the preprocessed data packetsin the cell group and a multiplication of the split ratio for the cellgroup and a size of the packets that are not preprocessed yet.

In the case where the UE performs a buffer status report for a certaincell group, the buffer status report may be configured to include onlythe total size of the preprocessed data packets in the correspondingcell groups. In the case where the UE performs a buffer status reportfor a certain cell group, it may also be possible for the UE toconfigure the buffer status report to include a multiplication of thetotal size of data stored in the PDCP entity and a split ratio for thecorresponding cell group. In the case where the UE performs a bufferstatus report for a certain cell group, it may also be possible for theUE to configure the buffer status report to include a size of data forthe corresponding cell group according to the split ratio in the totalsize of the data stored in the PDCP entity.

Embodiment 1-1 may be extended so as to be identically applied to amulti-connectivity situation as well as a dual connectivity situation.For example, the split ratio may be set in an extended format such as2:1:1 and 2:1:1:1 as well as the original format such as 2:1 forperforming the above-described preprocessing; the above-described BSRmay also be applied in the same manner

FIG. 1H is a diagram for explaining a data preprocessing method in adual connectivity split bearer environment in a next generation mobilecommunication system according to an embodiment of the disclosure.

Hereinafter a description is made of data preprocessing in the dualconnectivity split bearer environment in a next generation mobilecommunication system according to embodiment 1-2 of the disclosure.

The split bearer is a DRB that is capable of increasing a data rate byallowing a PDCP entity 1 h-05 to send data packets in a distributedmanner to two RLC entities 1 h-10 and 1 h-15 that transmit data throughdifferent cells.

According to an embodiment of the disclosure, the dual connectivityenvironment may include the scenarios 1 f-01, 1 f-02, 1 f-03, and 1 f-04of FIG. 1F of which each may be applicable to a situation of using adual connectivity downlink (DL) split bearer at a base station and asituation of using a dual connectivity uplink (UL) split bearer at a UE.The disclosure may be applied to the above scenarios.

In the case of using a split bearer in a dual connectivity environment,the PDCP entity 1 h-05 may process data packets (IP packets or PDCPSDUs) into PDCP PDUs and send the PDCP PDUs to a first RLC entity 1 h-10and a second RLC entity 1 h-15 according to a predetermined ratio.

The predetermined ratio may be determined by a network (or base stationof an MCG or an SCG) and transmitted to a UE via an RRC message (or anewly defined MAC CE or a newly defined PDCP control PDU) (in downlink,the PDCP entity of the MCG may immediately acquire information on thepredetermined ratio from the network). For example, the base station maytransmit the predetermined ratio and information on whether the firstand second RLC entities are established to the UE via theRRCConnectionSetup message at step 1 e-10 or theRRCConnectionReconfiguration message at steps 1 e-20 and 1 e-35 in FIG.1E.

In the case where the predetermined ratio is configured and the firstand second RLC entities are established, if a size of stored datapackets is less than threshold 2, the PDCP entity 1 h-05 may process thedata for one of the first and second RLC entities. If the RLC entity isan LTE RLC entity, it may store the data packets until transmissionresources are allocated; if the RLC entity is an NR RLC entity, it mayperform the data preprocessing process as described with reference toFIG. 1G.

In the above procedure, sending the data packets to the first and secondRLC entities may mean tagging the data packets with the MCG or the SCGaccording to the ratio and making a record thereof Here, it may bepossible to interpret that the MCG and SCG correspond respectively tothe first and second RLC entities.

If the size of the data packets stored in the PDCP entity 1 h-05 isgreater than threshold 2, the PDCP entity sends the data to the firstand second RLC entities 1 h-10 and 1 h-15 according to the predeterminedratio.

For example, if the predetermined ratio is set to 2:1, two data packetsare sent to the first RLC entity while one data packet is sent to thesecond RLC entity. The PDCP entity may repeat the above procedure. Thedata packets 1 g-10 sent to the first and second RLC entities may bepreprocessed into a MAC SDU 1 g-20 along with a MAC sub-header asdescribed with reference to FIG. 1G.

The data preprocessing process may be continuously performed when thetotal size of the preprocessed data packets is equal to or less than apredetermined threshold 1. If the total size of the preprocessed datapackets is equal to or greater than the predetermined threshold 1, thepreprocessing process may be stopped. If transmission resources areallocated and data transmission is completed such that the total size ofthe preprocessed data packets becomes less than the predeterminedthreshold 1, the preprocessing process may be resumed.

If transmission resources are allocated to the MCG or SCG for datatransmission, the MCG or SCG generates MAC PDUs fit in size to thetransmission resources with the preprocessed data packets and, if thesize of the transmission resources is less than the size of thepreprocessed data packets, it may segment the last MAC SDU, update theMAC sub-header correspondingly, and generate a MAC PDU.

Threshold 1 and threshold 2 may be determined by a network (or basestation of the MCG or SCG) and transmitted to a UE via an RRC message(or a newly defined MAC CE or a newly defined PDCP control PDU) (indownlink, the PDCP entity of the MCG may immediately acquire informationon threshold 1 and threshold 1 from the network).

For example, the base station may transmit threshold 1 and threshold 2to the UE via the RRCConnectionSetup message at step 1 e-10 or theRRCConnectionReconfiguration message at steps 1 e-20 and 1 e-35 of FIG.1E. Depending on UE capability, the UE may determine the valueautonomously. That is, the UE may set threshold 1 to a valuecorresponding to a size of the largest transport block (TB) or a TB fora highest data rate (highest rate TB).

The UE may also set threshold 1 to a value obtained by multiplying thehighest rate by a round trip time (RTT). The UE may also set threshold 2to a predetermined value. Threshold 1 and threshold 2 may each bedefined by a number of data packets or bytes indicative of data size.

In embodiment 1-2 of the disclosure, the PDCP entity 1 h-05, the RLCentities 1 h-10 and 1 h-15, and the MAC entities 1 h-20 and 1 h-25operate as follows.

If a first condition is fulfilled, the PDCP entity 1 h-05 follows afirst method; if a second condition and a third condition are fulfilled,the PDCP entity 1 h-05 follows a second method; if the second conditionand a fourth condition are fulfilled, the PDCP entity 1 h-05 follows athird method.

The first condition is that the PDCP entity receive data packets from ahigher layer and one of the first and second RLC entities is configuredto process and send the data packets or that the total size of the datapackets received by the PDCP entity is equal to or less than threshold 2or that the total size of the data packets received by the PDCP entityis less than threshold 2 even if both the first and second RLC entitiesare configured (information indicating whether the first RLC entityand/or the second RLC entity is configured and threshold 2 may bedetermined by the network (or base station of the MCG or SCG) andtransmitted to the UE via an RRC message (or a newly defined MAC CE or anewly defined PDCP control PDU (in downlink, the PDCP entity of the MCGmay directly acquire RLC entity configuration information and threshold2 from the network). For example, the base station may notify the UEwhether the first and second RLC entities are configured using theRRCConnectionSetup message at step 1 e-10 or theRRCConnectionReconfiguration message at steps 1 e-20 and 1 e-35 of FIG.1E.).

The second condition is that the PDCP entity receives data packets fromthe higher layer and both the first and second RLC entities areconfigured to process and send the data packets and the total size ofthe data packets received by the PDCP entity is greater than threshold 2(information indicating whether the first RLC entity and/or the secondRLC entity is configured and a value of threshold 2 may be determined bythe network (or base station of the MCG or SCG) and transmitted to theUE via an RRC message (or a newly defined MAC CE or a newly defined PDCPcontrol PDU) (in downlink, the PDCP entity of the MCG may directlyacquire RLC entity configuration information and threshold 2 from thenetwork). For example, the base station may notify the UE whether thefirst and second RLC entities are configured using theRRCConnectionSetup message at step 1 e-10 or theRRCConnectionReconfiguration message at steps 1 e-20 and 1 e-35 of FIG.1E.).

The third condition is that a ratio is predetermined and a size ofpreprocessed data packets is equal to or less than threshold 1.

The fourth condition is that a ratio is predetermined and a size ofpreprocessed data packets is greater than threshold 1.

In the first method, the PDCP entity processes the data packets from thehigher layer into PDCP PDUs and sends them to one of the first andsecond RLC entities that is configured to process and send data packets.

In the second method, the PDCP entity processes the data packets fromthe higher layer into PDCP PDUs and sends the PDCP PDUs to the first andsecond RLC entities according to a predetermined ratio.

In the third method, the PDCP entity holds the PDCP PDUs generated byprocessing the data packets from the higher layer without sending themto the first and second RLC entities and waits until the third conditionis fulfilled.

The RLC entities 1 h-10 and 1 h-15 follow the first method for the casewhere the first condition is fulfilled and the second method for thecase where the second condition is fulfilled.

The first condition is the case where the RLC entities are LTE RLCentities or eLTE RLC entities (the eLTE RLC entities are evolved LTE RLCentities updated with new or improved functions).

The second condition is the case where the RLC entities are NR RLCentities (NR RLC entities of the next generation mobile communicationsystem may be characterized by including the functions described withreference to FIG. 1D with the exception of the concatenation function.

In the first method, the RLC entities store the PDCP PDUs received fromthe PDCP entity, waiting until transmission resources are allocated,generate, if transmission resources are allocated, RLC PDUs byconcatenating the PDCP PDUs to be fit in size for the transmissionresources and adding RLC headers, and send the RLC PDUs to thecorresponding MAC entities.

In the second method, the RLC entities generate RLC PDUs with RLCheaders for data preprocessing on the PDCP PDUs received from the PDCPentity as described with reference to FIG. 1G regardless of transmissionresources allocation and send the RLC PDUs to the corresponding MACentities, the MAC entities generating MAC sub-headers and MAC SDUs tocomplete the data preprocessing.

The MAC entities 1 h-20 and 1 h-25 follow the first method for the casewhere the first condition is fulfilled and the second method for thecase where the second condition is fulfilled.

The first condition is the case where the MAC entities are LTE MACentities or eLTE MAC entities (the eLTE MAC entities are evolved LTE MACentities updated with new or improved functions).

The second condition is the case where the MAC entities are NR MACentities (NR MAC entities of the next generation mobile communicationsystem may include the functions described with reference to FIG. 1D).

In the first method, the MAC entities store the RLC PDUs received fromthe RLC entities, generate MAC PDUs with MAC sub-headers and MAC SDUs tobe fit in size for the transmission resources, and send the MAC PDUs tothe corresponding PHY entities.

In the second method, the MAC entities configure MAC sub-headers and MACSDUs by processing the RLC PDUs received from the RLC entities asdescribed with reference to FIG. 1G regardless of transmission resourcesallocation to complete the data preprocessing. If transmission resourcesare allocated, the MAC entities generate the MAC PDUs with the MACsub-headers and MAC SDUs to be fit in size for the transmissionresources and, if the size of the transmission resources is less thanrequired, segment the last MAC SDUs, update the MAC sub-headers, andsend the MAC PDUs to the corresponding PHY entities.

Threshold 1 may be set to a value corresponding to a size of the largesttransport block (TB) or a TB for a highest data rate (highest rate TB).Threshold 1 may also be set to a value obtained by multiplying thehighest rate by a round trip time (RTT). Threshold 2 may also be set toa predetermined value. Threshold 1 and threshold 2 may each be definedby a number of data packets or bytes indicative of a data size.

Threshold 1 indicates a data amount necessary to be preprocessed at theUE. That is, if IP packets are continuously passed down to the PDCPlayer in the UE, preprocessing is performed by an amount set bythreshold 1 rather than in a continuous manner Threshold 1 may make itpossible to avoid unnecessary preprocessing at the UE.

Because threshold 1 is set to a value corresponding to a maximum ULtransmission resource amount (UL grant)/maximum data size (maximum TB)available for the UE, the UE may be able achieve a preprocessing gainwithout any loss. If the maximum UL transmission resource amount (ULgrant)/maximum data size (maximum TB) available for the UE increases byemploying a certain technology such as carrier aggregation andmulti-connectivity, threshold 1 may be reset to a value in adaptation tothe increase.

Threshold 1 may also be set per bearer or connected cell or basestation. Threshold 1 may also be used in a single connectivitysituation, i.e., a case where the UE connects to one base station fordata communication, as well as multi-connectivity situation.

Threshold 2 is configured by the network and may be set to a value inconsideration of a data traffic amount of the network/a number ofactivated UEs (UEs in data communication or in the RRC connected mode)and, if a data traffic amount of the network/a number of activated UEs(UEs in data communication or in the RRC connected mode) is changed, itmay be reconfigured in adaptation to the change through the procedure oftransmitting the RRC Connection Reconfiguration message at step 1 e-35of FIG. 2E.

Threshold 2 aims to prevent the PDCP entity of the UE having a smallnumber of IP packets, i.e., a low data rate, from performingpreprocessing unnecessarily to transmit packets to respective cellgroups according to a predetermined split ratio. That is, the datapreprocessing is performed, only when the PDCP entity has the datagreater than threshold 2, i.e., the amount of data present in the PDCPentity is sufficient to use the dual connectivity technique, to transmitdata through respective cell groups for increasing the data rate.

Accordingly, if the data amount present in the PDCP entity is less thanthreshold 2, the PDCP entity may perform data preprocessing and BSR forone of the MCG and SCG. By using threshold 2 in a low data ratesituation, it is possible to avoid transmission resource waste caused bypadding (if the data amount is less than the least size of a TB(transmission resource) being transmitted at a low data rate, this leadsto padding, which may be decreased by performing data transmissionthrough one of the two cell groups).

Threshold 1 and threshold 2 are configured by the network and broadcastin the system information so as to set as default to UEs; if threshold 1and threshold 2 are configured through the RRC Connection Setup, RRCConnection Resume, or RRC connection Reconfiguration procedure at steps1 e-10, 1 e-20, or 1 e-35 of FIG. 1E, the UE may apply the thresholdvalues received via this procedure preferentially rather than thedefault value broadcast in the system information.

In embodiment 1-2 of the disclosure, the preprocessed data packets maybe canceled in a predetermined case. That is, it may be possible todiscard the preprocessed data packets and process original data packets(PDCP SDUs) stored in the PDCP entity according to embodiment 1-2. Thepredetermined case may be the case where the PDCP entity or the RLCentities are reset or reestablished, RLC entities are newly established,or the operation of the PDCP entity is changed according to threshold 2.

In embodiment 1-2 of the disclosure, if it is necessary for the UE toperform a buffer status report, i.e., if the UE has to make a bufferstatus report for a certain cell group, the UE may configure the bufferstatus report by summing the total size of the preprocessed data packetsin the cell group and a multiplication of the split ratio for the cellgroup and a size of the packets that are not preprocessed yet.

In the case where the UE performs a buffer status report for a certaincell group, the buffer status report may be configured to include onlythe total size of the preprocessed data packets in the correspondingcell groups. In the case where the UE performs a buffer status reportfor a certain cell group, it may also be possible for the UE toconfigure the buffer status report to include a multiplication of thetotal size of data stored in the PDCP entity and a split ratio for thecorresponding cell group. In the case where the UE performs a bufferstatus report for a certain cell group, it may also be possible for theUE to configure the buffer status report to include a size of data forthe corresponding cell group according to the split ratio in the totalsize of the data stored in the PDCP entity.

Embodiment 1-1 may be extended so as to be applied identically to amulti-connectivity situation as well as a dual connectivity situation.For example, the split ratio may be set in an extended format such as2:1:1 and 2:1:1:1 as well as the original format such as 2:1 forperforming the above-described preprocessing; the above-described BSRmay also be applied in the same manner

In embodiment 1-1 or 1-2 of the disclosure, the predetermined splitratio or threshold 1 may be configured to UEs via the system informationbroadcast by the network as default, the RRCConnectionSetup message, orthe RRCConnectionReconfiguration message being transmitted from the basestation to the UE at step 1 e-10, 1 e-20, or 1 e-35 in FIG. 1E, or anewly defined MAC CE or a newly defined PDCP control PDU.

In the case where the base station configures a split bearer, i.e., anMCG and an SCG, to the UE, it may set the PDCP configuration information(PDCP-config) included the RRC Connection Setup, RRC Connection Resume,or RRC connection Reconfiguration message at steps 1 e-10, 1 e-20, or 1e-35 of FIG. 1E to a ul-DataSplitDRB-ViaSCG value or aul-DataSplitThreshold value.

PDCP-Config

The PDCP-Config information element is used for configuring variablePDCP parameters for data radio bearers.

PDCP-Config information element

-- ASN1START PDCP-Config ::= SEQUENCE { discardTimer ENUMERATED { ms50,ms100, ms150, ms300, ms500, ms750, ms1500, infinity } OPTIONAL, -- CondSetup rlc-AM SEQUENCE { statusReportRequired BOOLEAN } OPTIONAL, -- CondRlc-AM rlc-UM SEQUENCE { pdcp-SN-Size ENUMERATED {len7bits, len12bits} }OPTIONAL, -- Cond Rlc-UM headerCompression CHOICE { notUsed NULL, rohcSEQUENCE { maxCID INTEGER {1..16383} DEFAULT 15, profiles SEQUENCE {profile0x0001 BOOLEAN, profile0x0002 BOOLEAN, profile0x0003 BOOLEAN,profile0x0004 BOOLEAN, profile0x0006 BOOLEAN, profile0x0101 BOOLEAN,profile0x0102 BOOLEAN, profile0x0103 BOOLEAN, profile0x0104 BOOLEAN },... } }, ..., [[ rn-IntegrityProtection-r10 ENUMERATED {enabled}OPTIONAL -- Cond RN ]], [[ pdcp-SN-Size-v1130 ENUMERATED {len15bits}OPTIONAL  -- Cond Rlc-AM2 ]], [[ ul-DataSplitDRB-ViaSCG-r12BOOLEAN OPTIONAL, -- Need ON t-Reordering-r12 ENUMERATED { ms0, ms20,ms40, ms60, ms80, ms100, ms120, ms140, ms160, ms180, ms200, ms220,ms240, ms260, ms280, ms300, ms500, ms750, spare14, spare13, spare12,spare11, spare10, spare9, spare8, spare7, spare6, spare5, spare4,spare3, spare2, spare1} OPTIONAL -- Cond setupS ]], [[ul-DataSplitThreshold-r13 CHOICE { release NULL, setup ENUMERATED { b0,b100, b200, b400, b800, b1600, b3200, b6400, b12800, b25600, b51200,b102400, b204800, b409600, b819200, infinity spare1} }  OPTIONAL, --Need ON pdcp-SN-Size-v1310 ENUMERATED {len18bits} OPTIONAL,  -- CondRlc-AM3 statusFeedback-r13 CHOICE { release NULL, setup SEQUENCE {statusPDU-TypeForPolling-r13 ENUMERATED {type1, type2} OPTIONAL, -- NeedON statusPDU-Periodicity-Type1-r13 ENUMERATED { ms5, ms10, ms20, ms30,ms40, ms50, ms60, ms70, ms80, ms90, ms100, ms150, ms200, ms300, ms500,ms1000, ms2000, ms5000, ms10000, ms20000, ms50000} OPTIONAL, -- Need ONstatusPDU-Periodicity-Type2-r13 ENUMERATED { ms5, ms10, ms20, ms30,ms40, ms50, ms60, ms70, ms80, ms90, ms100, ms150, ms200, ms300, ms500,ms1000, ms2000, ms5000, ms10000, ms20000, ms50000} OPTIONAL, -- Need ONstatusPDU-Periodicity-Offset-r13 ENUMERATED { ms1, ms2, ms5, ms10, ms25,ms50, ms100, ms250, ms500, ms2500, ms5000, ms25000} OPTIONAL -- Need ON} } OPTIONAL  -- Need ON ]] } -- ASN1STOP

Table 1a, Table 1b, and Table 1c describe fields included in thePDCP-Config information element.

TABLE 1a discardTimer Indicates the discard timer value specified in TS36.323 [8], Value in milliseconds. Value ms50 means 50 ms, and ms100means 100 ms. headerCompression E-UTRAN does not reconfigure headercompression for an MCG DRB except upon the first reconfiguration andupon handover after RRC connection reestablishment. E-UTRAN does notreconfigure header compression for an SCG DRB except upon SCG changeinvolving PDCP reestablishment. For split and LTE-WLAN Aggregation (LWA)DRBs, E-UTRAN configures only notUsed. maxCID Indicates the value of theMAX_CID parameter as specified in TS 36.323 [8], The total value ofMAX_CIDs across all bearers for the UE should be less than or equal tothe value of the maxNumberROHC-ContextSessions parameter as indicated bythe UE. pdcp-SN-Size Indicates the PDCP Sequence Number length in bits.For RLC UM (Unacknowledged Mode): value len7 bits means that the 7-bitPDCP SN format is used and len12 bits means that the 12-bit PDCP SNformat is used. For RLC AM (Acknowledged Mode): value len15 bits meansthat the 15-bit PDCP SN format is used, value len18 bits means that the18-bit PDCP SN format is used, otherwise if the field is not includedupon setup of the PCDP entity, 12-bit PDCP SN format is used, asspecified in TS 36.323 [8].

TABLE 1b profiles The profiles used by both compressor and decompressorin both UE and E-UTRAN. The field indicates which of the ROHC profilesspecified in TS 36.323 [8] are supported, i.e., value true indicatesthat the profile is supported. Profile 0x0000 shall always be supportedwhen the use of ROHC is configured. If support of two ROHC profileidentifiers with the same 8 LSB's is signaled, only the profilecorresponding to the highest value shall be applied. E-UTRAN does notconfigure ROHC while t- Reordering is configured (i.e., for split DRBsor upon reconfiguration from split to MCG DRB). statusFeedback Indicateswhether the UE shall send PDCP Status Report periodically or by E- UTRANpolling as specified in TS 36.323 [8]. statusPDU-TypeForPollingIndicates the PDCP Control PDU option when it is triggered by E-UTRANpolling. Value type1 indicates using the legacy PDCP Control PDU forPDCP status reporting and value type2 indicates using the LWA specificPDCP Control PDU for LWA status reporting as specified in TS 36.323 [8].statusPDU-Periodicity-Type1 Indicates the value of the PDCP Statusreporting periodicity for type1 Status PDU, as specified in TS 36.323[8]. Value in milliseconds. Value ms5 means 5 ms, and ms10 means 10 ms.

TABLE 1c statusPDU-Periodicity-Type2 Indicates the value of the PDCPStatus reporting periodicity for type2 Status PDU, as specified in TS36.323 [8], Value in milliseconds. Value ms5 means 5 ms, and ms10 means10 ms. statusPDU-Periodicity-Offset Indicates the value of the offsetfor type2 Status PDU periodicity, as specified in TS 36.323 [8]. Valuein milliseconds. Value ms1 means 1 ms, and ms2 means 2 ms. t-ReorderingIndicates the value of the reordering timer, as specified in TS 36.323[8], Value in milliseconds. Value ms0 means 0 ms, and ms20 means 20 ms.rn-IntegrityProtection Indicates that integrity protection orverification shall be applied for all subsequent packets received andsent by the radio network (RN) on the DRB. statusReportRequiredIndicates whether or not the UE shall send a PDCP Status Report upon re-establishment of the PDCP entity and upon PDCP data recovery asspecified in TS 36.323 [8]. ul-DataSplitDRB-ViaSCG Indicates whether theUE shall send PDCP PDUs via SCG as specified in TS 36.323 [8]. E-UTRANonly configures the field (i.e. indicates value TRUE) for split DRBs.ul-DataSplitThreshold Indicates the threshold value for uplink datasplit operation specified in TS 36.323 [8], Value b100 means 100 Bytes,and b200 means 200 Bytes. E-UTRAN only configures this field for splitDRBs.

In the case where ul-DataSplitDRB-ViaSCG is set to TRUE, if the size ofthe data available for transmission (or UL or DL data rate) is less thanul-DataSplitThreshold, the UE attempts data transmission (e.g., sendsbuffer status report (BSR)) and performs data transmission (datapreprocessing may be performed) only via SCG.

If the size of the data available for transmission (or UL or DL datarate) is greater than or equal to ul-DataSplitThreshold, the UE attemptsdata transmission (e.g., sends BSR) and performs data transmission (datapreprocessing may be performed) via MCG or SCG (or both the groups).

In the case where ul-DataSplitDRB-ViaSCG is set to FALSE orul-DataSplitDRB-ViaSCG is not configured, if the size of the dataavailable for transmission (or UL or DL data rate) is less than theul-DataSplitThreshold, the UE attempts data transmission (e.g., sendsBSR) and performs data transmission (data preprocessing may beperformed) only via MCG.

If the size of the data available for transmission (or UL or DL datarate) is greater than or equal to ul-DataSplitThreshold, the UE attemptsdata transmission (e.g., sends BSR) and performs data transmission (dataprocessing may be performed) via MCG or SCG (or both the groups).

In the disclosure, ul-DataSplitThreshold may be set to a predeterminedspecific value such that the UE attempts data transmission only via thecell group indicated by ul-DataSplitThreshold and performs datatransmission. That is, if ul-DataSplitThreshold is set to infinity (or0, if 0 is designated as the predetermined specific value), the UEalways attempts data transmission (e.g., sends BSR) and performs datatransmission (data preprocessing may be performed) only via the cellgroup indicated by ul-DataSplitDRB-ViaSCG regardless of the size of dataavailable for transmission (or UL or DL data rate).

That is, if ul-DataSplitDRB-ViaSCG=TRUE andul-DataSplitThreshold=infinity, the UE always attempts data transmission(e.g., sends BSR) and performs data transmission (data preprocessing maybe performed) only via SCG. If ul-DataSplitDRB-ViaSCG=FALSE (notconfigured) and ul-DataSplitThreshold=infinity, the UE always attemptsdata transmission (e.g., sends BSR) and performs data transmission (datapreprocessing may be performed) only via MCG.

A command for instructing the UE to attempt and perform datatransmission to one cell group may be dynamically delivered using anewly defined MAC CE or PDCP PDU.

FIGS. 1IA to FIG. 1IC are flowcharts illustrating operations of PDCP,RLC, and MAC entities in a UE.

In FIG. 1IA, the PDCP entity of the UE starts operating at step 1 i-01and, if receiving data packets from a higher layer at step 1 i-11, itchecks, at step 1 i-12, for a first condition, a second condition, athird condition, and a fourth condition. If the first condition isfulfilled, the PDCP entity applies a first method at step 1 i-13; if thesecond and third conditions are fulfilled, the PDCP entity applies asecond method at step 1 i-14; if the second and fourth conditions arefulfilled, the PDCP entity applies a third method at step 1 i-15.

In FIG. 1IB, the RLC entity of the UE starts operating at step 1 i-02and, if receiving data packets from the higher layer at step 1 i-21,checks for the first and second conditions at step 1 i-22. If the firstcondition is fulfilled, the RLC entity applies the first method at step1 i-23; if the second condition is fulfilled, the RLC entity applies thesecond method at step 1 i-24.

In FIG. 1IC, the MAC entity of the UE starts operating at step 1 i-03and, if receiving data packets from a higher layer at step 1 i-31,checks for the first and second conditions at step 1 i-32. If the firstcondition is fulfilled, the MAC entity applies the first method at step1 i-33; if the second condition is fulfilled, the MAC entity applies thesecond method at step 1 i-34.

FIG. 1J shows operations of a PDCP entity for sending data packets to afirst RLC entity and a second RLC entity according to a predeterminedsplit ratio, in embodiments 1-1 and 1-2 that embody methods forpreprocessing data in a dual connectivity split bearer environment in anext generation mobile communication system, according to embodiment1-3-1 of the disclosure.

FIG. 1J is a diagram illustrating an order and a method for a PDCPentity to send data packets to a first RLC entity and a second RLCentity according to a predetermined ratio. In the disclosure, it isassumed that the predetermined ratio between the first and second RLCentities is 3:1.

Even when the predetermined ratio is given as x:y, embodiment 1-3-1 maybe applied in the same manner In the disclosure, it is assumed that theratio is 3:1 for convenience of explanation.

In embodiment 1-3-1 of the disclosure, the PDCP entity assigns 3 packetsto the first RLC entity at step 1 j-05 and 1 packet to the second RLCentity at step 1 j-10 according to the ratio of 3:1. Next, the PDCPentity assigns 3 packets to the first RLC entity at step 1 j-15 and 1packet to the second RLC entity at step 1 j-20 again to keep the ratioof 3:1. In embodiment 1-3-1, this procedure is repeated with the packetsfrom the higher layer.

FIG. 1K shows operations of a PDCP entity for sending data packets to afirst RLC entity and a second RLC entity according to a predeterminedsplit ratio, in embodiments 1-1 and 1-2 that embody methods forpreprocessing data in a dual connectivity split bearer environment in anext generation mobile communication system, according to embodiment1-3-2 of the disclosure.

FIG. 1K is a diagram illustrating an order and a method for a PDCPentity to send data packets to a first RLC entity and a second RLCentity according to a predetermined ratio. In the disclosure, it isassumed that the predetermined ratio between the first and second RLCentities is 3:1.

Even when the predetermined ratio is given as x:y, embodiment 1-3-2 maybe applied in the same manner In the disclosure, it is assumed that theratio is 3:1 for convenience of explanation. In embodiment 1-3-2 of thedisclosure, the PDCP entity assigns 3 packets to the first RLC entity atstep 1 k-05 and 1 packet to the second RLC entity at step 1 k-10according to the ratio of 3:1. Next, the PDCP entity assigns 1 packet tothe second RLC entity at step 1 k-15 and 3 packets to the first RLCentity at step 1 k-20 to keep the ratio of 3:1. In embodiment 1-3-2,this procedure is repeated with the packets from the higher layer.

FIG. 1L shows operations of a PDCP entity for sending data packets to afirst RLC entity and a second RLC entity according to a predeterminedsplit ratio, in embodiments 1-1 and 1-2 that embody methods forpreprocessing data in a dual connectivity split bearer environment in anext generation mobile communication system, according to embodiment1-3-3 of the disclosure.

FIG. 1L is a diagram illustrating an order and a method for a PDCPentity to send data packets to a first RLC entity and a second RLCentity according to a predetermined ratio. In the disclosure, it isassumed that the predetermined ratio between the first and second RLCentities is 3:1.

Even when the predetermined ratio is given as x:y, embodiment 1-3-3 maybe applied in the same mariner In the disclosure, it is assumed that theratio is 3:1 for convenience of explanation. In embodiment 1-3-3, thePDCP entity assigns 1 packet to the second RLC entity at step 11-05 and3 packets to the first RLC entity at step 11-10 according to the ratioof 3:1. Next, the PDCP entity assigns 1 packet to the second RLC entityat step 11-15 and 3 packets to the first RLC entities at step 11-20 tokeep the ratio of 3:1. In embodiment 1-3-3, this procedure is repeatedwith the packets from the higher layer.

FIG. 1M shows operations of a PDCP entity for sending data packets to afirst RLC entity and a second RLC entity according to a predeterminedsplit ratio, in embodiments 1-1 and 1-2 that embody methods forpreprocessing data in a dual connectivity split bearer environment in anext generation mobile communication system, according to embodiment1-3-4 of the disclosure.

FIG. 1M is a diagram illustrating an order and a method for a PDCPentity to send data packets to a first RLC entity and a second RLCentity according to a predetermined ratio. In the disclosure, it isassumed that the predetermined ratio between the first and second RLCentities is 3:1.

Even when the predetermined ratio is given as x:y, embodiment 1-3-4 maybe applied in the same manner In the disclosure, it is assumed that theratio is 3:1 for convenience of explanation. In embodiment 1-3-4, thePDCP entity first assigns 1 packet to the second RLC entity at step 1m-05 and 3 packets to the first RLC entity at step 1 m-10 according tothe ratio of 3:1. Next, the PDCP entity first assigns 3 packets to thefirst RLC entity at step 1 m-15, 1 packet to the second entity at step 1m-20, 1 packet to the second RLC entity at step 1 m-25, and 3 packets tothe first RLC entity at step 1 m-30 to keep the ratio of 3:1. Inembodiment 1-3-4, this procedure is repeated with the packets from thehigher layer.

FIG. 1N shows operations of a PDCP entity for sending data packets to afirst RLC entity and a second RLC entity according to a predeterminedsplit ratio, in embodiments 1-1 and 1-2 that embody methods forpreprocessing data in a dual connectivity split bearer environment in anext generation mobile communication system, according to embodiment1-3-5 of the disclosure.

FIG. 1N is a diagram illustrating an order and a method for a PDCPentity to send data packets to a first RLC entity and a second RLCentity according to a predetermined ratio. In the disclosure, it isassumed that the predetermined ratio between the first and second RLCentities is 3:1.

Even when the predetermined ratio is given as x:y, embodiment 1-3-5 maybe applied in the same manner In the disclosure, it is assumed that theratio is 3:1 for convenience of explanation. In embodiment 1-3-5, thePDCP entity first assigns 1 packet to the first RLC entity and then 1packet to the second RLC entity at step 1 n-05 and assigns 2 packets tothe first RLC entity at step 1 n-10 according to the ratio of 3:1. Next,the PDCP entity first assigns 1 packet to the first RLC entity and then1 packet to the second RLC entity at step 1 n-15 and assigns 2 packetsto the first RLC entity at step 1 n-20 to keep the ratio of 3:1. Inembodiment 1-3-5, this procedure is repeated with the packets from thehigher layer.

FIG. 1O shows operations of a PDCP entity for sending data packets to afirst RLC entity and a second RLC entity according to a predeterminedsplit ratio, in embodiments 1-1 and 1-2 that embody methods forpreprocessing data in a dual connectivity split bearer environment in anext generation mobile communication system, according to embodiment1-3-6 of the disclosure.

FIG. 1O is a diagram illustrating an order and a method for a PDCPentity to send data packets to a first RLC entity and a second RLCentity according to a predetermined ratio. In the disclosure, it isassumed that the predetermined ratio between the first and second RLCentities is 3:1.

Even when the predetermined ratio is given as x:y, embodiment 1-3-6 maybe applied in the same manner In the disclosure, it is assumed that theratio is 3:1 for convenience of explanation. In embodiment 1-3-6, thePDCP entity first assigns 1 packet to the first RLC entity and then 1packet to the second RLC entity at step 1 o-05 and assigns 2 packets tothe first RLC entity at step 1 o-10. Net, the PDCP entity first assigns1 packet to the second RLC entity and then 1 packet to the first RLCentity at step 1 o-15 and assigns 2 packets to the first RLC entity atstep 1 o-20 to keep the ratio of 3:1. In embodiment 1-3-6, thisprocedure is repeated with the packets from the higher layer.

FIG. 1P shows operations of a PDCP entity for sending data packets to afirst RLC entity and a second RLC entity according to a predeterminedsplit ratio, in embodiments 1-1 and 1-2 that embody methods forpreprocessing data in a dual connectivity split bearer environment in anext generation mobile communication system, according to embodiment1-3-7 of the disclosure.

FIG. 1P is a diagram illustrating an order and a method for a PDCPentity to send data packets to a first RLC entity and a second RLCentity according to a predetermined ratio. In the disclosure, it isassumed that the predetermined ratio between the first and second RLCentities is 3:1.

Even when the predetermined ratio is given as x:y, embodiment 1-3-7 maybe applied in the same manner In the disclosure, it is assumed that theratio is 3:1 for convenience of explanation. In embodiment 1-3-7, thePDCP entity first assigns 1 packet to the second RLC entity and then 1packet to the first entity at step 1 p-05 and assigns 2 packets to thefirst RLC entity at step 1 p-10 according to the ratio of 3:1. Next, thePDCP entity first assigns 1 packet to the first RLC entity and then 1packet to the second RLC entity at step 1 p-15 and assigns two packetsto the first RLC entity at step 1 p-20 to keep the ratio of 3:1. Inembodiment 1-3-7, this procedure is repeated with the packets from thehigher layer.

FIG. 1Q shows operations of a PDCP entity for sending data packets to afirst RLC entity and a second RLC entity according to a predeterminedsplit ratio, in embodiments 1-1 and 1-2 that embody methods forpreprocessing data in a dual connectivity split bearer environment in anext generation mobile communication system, according to embodiment1-3-8 of the disclosure.

FIG. 1Q is a diagram illustrating an order and a method for a PDCPentity to send data packets to a first RLC entity and a second RLCentity according to a predetermined ratio. In the disclosure, it isassumed that the predetermined ratio between the first and second RLCentities is 3:1.

Even when the predetermined ratio is given as x:y, embodiment 1-3-8 maybe applied in the same mariner In the disclosure, it is assumed that theratio is 3:1 for convenience of explanation. In embodiment 1-3-8, thePDCP entity first assigns 1 packet to the second RLC entity and then 1packet to the first entity at step 1 q-05 and assigns 2 packets to thefirst RLC entity at step 1 q-10. Next, the PDCP entity first assigns 1packet to the second RLC entity and then 1 packet to the first RLCentity at step 1 q-15 and assigns 2 packets to the first RLC entity atstep 1 q-20 to keep the ratio of 3:1. In embodiment 1-3-8, thisprocedure is repeated with the packets from the higher layer.

FIG. 1R is a block diagram illustrating a configuration of a UEaccording to an embodiment of the disclosure.

In reference to FIG. 1R, the UE includes a radio frequency (RF)processing unit 1 r-10, a baseband processing unit 1 r-20, a memory 1r-30, and a controller 1 r-40.

The RF processing unit 1 r-10 takes charge of signal band conversion andamplification for transmitting signals over a radio channel. That is,the RF processing unit 1 r-10 up-converts a baseband signal output fromthe baseband processing unit 1 r-20 to an RF band signal fortransmission through an antenna and down-converts an RF band signalreceived through the antenna to a baseband signal. For example, the RFprocessing unit 1 r-10 may include a transmission filter, a receptionfilter, an amplifier, a mixer, an oscillator, a digital-to-analogconverter (DAC), and an analog-to-digital convertor (ADC). Although oneantenna is depicted in the drawing, the terminal may include a pluralityof antennas.

The RF processing unit 1 r-10 may include a plurality of RF chains. TheRF processing unit 1 r-10 may perform beamforming For beamforming, theRF processing unit 1 r-10 may adjust the phases and sizes of the signaltransmitted/received through the antennas or antenna elements. The RFprocessing unit 1 r-10 may perform a MIMO operation to receive a signalon multiple layers.

The RF processing unit 1 r-10 may configure a plurality of antennas orantenna elements appropriately to perform reception beam sweeping andadjust a reception direction and width for matching with thetransmission beam under the control of the controller.

The baseband processing unit 1 r-20 takes charge of conversion betweenbaseband signals and bit strings according to a physical layer protocolof the system. For example, the baseband processing unit 1 r-20 performsencoding and modulation on the transmit bit strings to generate complexsymbols in data transmission mode.

The baseband processing unit 1 r-20 also performs demodulation anddecoding on a baseband signal from the RF processing unit 1 r-10 torecover the received bit strings in data reception mode. For the case ofan orthogonal frequency division multiplexing (OFDM) system, thebaseband processing unit 1 r-20 performs encoding and modulation on thetransmit bit string to generate complex symbols, maps the complexsymbols to subcarriers, performs inverse fast Fourier transform (IFFT)on the subcarriers, and inserts a cyclic prefix (CP) to generate OFDMsymbols in the data transmission mode.

The baseband processing unit 1 r-20 splits the baseband signal from theRF processing unit 1 r-10 into OFDM symbols, recovers the signals mappedto the subcarriers through fast Fourier transform (FFT), and performsdemodulation and decoding to recover the bit strings in the datareception mode.

The baseband processing unit 1 r-20 and the RF processing unit 1 r-10take charge of transmitting and receiving signals as described above.Accordingly, the baseband processing unit 1 r-20 and the RF processingunit 1 r-10 may be referred to as a transmission unit, a reception unit,a transceiver, or a communication unit. At least one of the basebandprocessing unit 1 r-20 and the RF processing unit 1 r-10 may include aplurality of communication modules for supporting different radio accesstechnologies.

At least one of the baseband processing unit 1 r-20 and the RFprocessing unit 1 r-10 may include a plurality of communication modulesfor processing different frequency band signals. Examples of the radioaccess technologies include WLAN (e.g., IEEE 802.11) and cellularnetwork (e.g., LTE). Examples of the different frequency bands mayinclude super high frequency (SHF) band (e.g., 2.5 GHz and 5 GHz) andmillimeter wave (mmWave) bands (e.g., 60 GHz).

The memory 1 r-30 stores basic programs for operation of the terminal,application programs, and data such as configuration information. Thememory 1 r-30 provides the stored data in response to a request from thecontroller 1 r-40.

The controller 1 r-40 controls overall operations of the terminal. Forexample, the controller 1 r-40 controls the baseband processing unit 1r-20 and the RF processing unit 1 r-10 to transmit/receive signals. Thecontroller 1 r-40 also writes and reads data to and from the memory 1r-30. In order to accomplish this, the controller 1 r-40 may include atleast one processor. For example, the controller 1 r-40 may include acommunication processor (CP) for controlling communication and anapplication processor (AP) for providing higher layer processing, e.g.,application layer protocol processing.

FIG. 1S is a block diagram illustrating a TRP in a wirelesscommunication system according to an embodiment of the disclosure.

As shown in the drawing, the base station includes an RF processing unit1 s-10, a baseband processing unit 1 s-20, a backhaul communication unit1 s-30, a memory 1 s-40, and a controller 1 s-50.

The RF processing unit 1 s-10 takes charge of signal band conversion andamplification for transmitting signals over a radio channel. That is,the RF processing unit 1 s-10 up-converts a baseband signal output fromthe baseband processing unit 1 s-20 to an RF band signal fortransmission through antennas and down-converts an RF band signalreceived through the antennas to a baseband signal.

For example, the RF processing unit 1 s-10 may include a transmissionfilter, a reception filter, an amplifier, a mixer, an oscillator, a DAC,and an ADC. Although one antenna is depicted in FIG. 1S, the basestation may include a plurality of antennas. The RF processing unit 1s-10 may include a plurality of RF chains. The RF processing unit 1 s-10may perform beamforming For beamforming, the RF processing unit 1 s-10may adjust the phases and sizes of the signal transmitted/receivedthrough the antennas or antenna elements. The RF processing unit 1 s-10may perform a downlink MIMO operation to transmit a signal on multiplelayers.

The baseband processing unit 1 s-20 takes charge of converting betweenbaseband signals and bit strings according to a physical layer protocolof the system. For example, the baseband processing unit 1 s-20 performsencoding and modulation on the transmit bit strings to generate complexsymbols in data transmission mode. The baseband processing unit 1 s-20also performs demodulation and decoding on the baseband signal from theRF processing unit 1 s-10 to recover the received bit strings in datareception mode.

For the case of an OFDM system, the baseband processing unit 1 s-20performs encoding and modulation on the transmit bit string to generatecomplex symbols, maps the complex symbols to subcarriers, performs IFFTon the subcarriers, and inserts a CP to generate OFDM symbols in thedata transmission mode. The baseband processing unit 1 s-20 splits thebaseband signal from the RF processing unit 1 s-10 into OFDM symbols,recovers the signals mapped to the subcarriers through FFT, and performsdemodulation and decoding to recover the bit strings in the datareception mode.

The baseband processing unit 1 s-20 and the RF processing unit 1 s-10take charge of transmitting and receiving signals as described above.Accordingly, the baseband processing unit 1 s-20 and the RF processingunit 1 s-10 may be referred to as a transmission unit, a reception unit,a transceiver, or a communication unit.

The backhaul communication unit 1 s-30 provides an interface forcommunication with other network nodes.

The memory 1 s-40 stores basic programs for operation of the basestation, application programs, and data such as configurationinformation. In particular, the memory 1 s-40 may store the informationon the bearers allocated to the connected terminal and a measurementresult reported by the terminal. The memory 1 s-40 may also store theinformation as criteria for determining whether to enable or disablemulti-connectivity for the terminal. The memory 1 s-40 provides thestored data in response to a request from the controller 1 s-50.

The controller 1 s-50 may control overall operations of the basestation. For example, the controller 1 s-50 controls the basebandprocessing unit 1 s-20, the RF processing unit 1 s-10, and the backhaulcommunication unit 1 s-30 for transmitting/receiving signals. Thecontroller 1 s-50 also writes and reads data to and from the memory 1s-40. In order to accomplish this, the controller 1 s-50 may include atleast one processor.

Second Embodiment

In the following description, the term “dual-registered” denotes that aUE is registered with two or more mobile communication systems toreceive a service. In the legacy LTE system, a UE in a registered state,i.e., EMM-registered state, may be in a standby mode or a connected modeat the RRC level. In the disclosure, a similar principle is assumed forthe next generation mobile communication system. The dual-registeredtechnique may be exploited for inter-system handover or carrieraggregation between heterogeneous systems.

FIG. 2A is a diagram for conceptually explaining the inter-systemhandover by applying a dual-registered technique in a next generationmobile communication system.

In the legacy inter-system handover, a source system requests to atarget system for a handover using a backhaul network. If the targetsystem accepts the request, it prepares resources for a UE to be handedover and transmits configuration information necessary for the handoverto the source system. The source system provides the UE moving to thetarget system with the configuration information necessary for thehandover.

In the case of applying the dual-registered technique to inter-systemhandover, when a UE moves from one system to another system, it performsan attach procedure to the target system rather than the legacy handoverprocedure. In the disclosure, a base station of a next generation mobilecommunication system is referred to as gNB, and a base station of theLTE system is referred to as eNB. The term “attach” denotes a procedurefor a UE to register itself with a system. In this case, the UE maymaintain its connection to a previous source system.

The dual-registered technique is advantageous in terms of negating theneed of an interoperation between the source and target systems that isperformed in legacy handover technologies. This means minimizing thenecessity of defining inter-system interfaces and upgrading legacysystems and makes it possible to reduce inter-system signaling overhead.

In order to support the dual-registered technique, the networks of thesource and target systems are connected to a network (NW) entity calledcommon IP anchor, which routes data from a data network to a UE.

Whether to maintain the connection to the old source system depends onthe capability of the UE. If the UE has multiple radios, it is notnecessary to break connection to the source system under the constraintof the number of radios. Typically, in the legacy LTE system, a fewhundred ms are required. Thus, if the UE communicates necessary datawhile maintaining the connection to the old source system, no serviceinterruption occurs in the middle of the attach operation. However, ifthe UE has one radio, the connection to the source system may not bemaintained. This means that the UE may not be served by the sourcesystem because the radio should be used for attaching to the targetsystem. Even in this case, it may be possible to maintain the connectionto the source system via time division multiplexing (TDM). However, thismay cause a certain degree of service quality degradation such as timedelay and data rate reduction.

FIG. 2B is a signal flow diagram illustrating signal flows in a casewhere a UE moves from a service area of a next generation mobilecommunication system to a service area of a legacy stem system accordingto an embodiment of the disclosure.

A gNB 2 b-04 and a UE 2 b-02 located in the service area of the gNB 2b-04 exchange their capability information indicating whether theysupport dual registration at step 2 b-13. The gNB notifies UEs locatedwithin its service area whether the next generation mobile communicationsystem supports dual-registration by broadcasting system information.The UE notifies the gNB whether it supports dual registration viadedicated signaling.

At step 2 b-14, the gNB configures LTE frequency measurement to the UE.The configuration information may include an LTE frequency measurementperiodicity and a time period for measuring on the LTE frequency at theperiodicity. Upon receipt of the configuration information, the UE mayperform measurement on the LTE frequency during the measurement periodat step 1 b-16. The UE may also perform measurement on the LTE frequencyat an appropriate timing that is autonomously determined. An example ofthe appropriate timing is a time period during which no data areexchanged with the gNB.

In order to perform measurement on the LTE frequency, the UE turns on anLTE modem. If the UE has a dual radio, it may maintain the turn-on stateof the LTE modem or turn on and off the LTE modem for starting andending the measurement at every LTE frequency measurement occasion.Alternatively, the UE supporting dual registration may performmeasurement on the LTE frequency without any configuration from the gNB.However, in this case, the UE may be able to perform measurement on theLTE frequency only at appropriate timings that are autonomouslydetermined by itself.

The UE reports a measurement result to the gNB at step 2 b-18. The gNBdetermines at step 2 b-20 whether to configure dual registration orinter-RAT (Radio Access Technology) handover based on the measurementresult and other information.

The gNB configures dual registration to the UE at step 2 b-22. In thiscase, a dedicated control plane message (dual-registered initialization)is used. Upon receipt of this message, the UE performs dualregistration.

This message may include information on a frequency or cell of the LTEsystem to which the UE has to attempted to attach. It may also bepossible for this message to provide a list of frequencies or cells inorder for the UE to select one of the frequencies or cells contained inthe list and attach thereto. The frequency or cell may be identifiedwith a frequency bandwidth, center frequency information, or a cell ID(Physical cell ID or ECGI). In order to reduce the time required for theUE to attach, the message may include partial system information of anLTE system cell 2 b-06. The partial system information is essentialinformation for use in accessing a target system. The essential systeminformation is information belonging to MIB, SIB1, SIB2, SIB3, SIB4, andSIBS being broadcast by the LTE cell.

In more detail, the information may include a list of public land mobilenetworks (PLMNs) supported by the LTE system cell, a tracking area code,a closed subscriber group (CSG) cell ID, a list of frequency bandssupported by a target system cell and spectrum emission information,access barring-related information (e.g., ACB, EAB, SSAC, and ACDC),configuration information associated with random access to the LTEsystem cell, and cell reselection prioritization information.

The essential system information of the LTE system cell may be reportedalong with a cell measurement report according to a request from thegNB, or the gNB may always collect system information of neighboring LTEsystem cells from specific UEs within a service area using aself-configuring and self-optimizing network (SON) technology.

Upon receipt of the dual-registered initialization message, the UEstarts a predetermined timer at step 2 b-24. If the UE that has receivedthe dual-registered initialization message has the dual radio, it mayperform attach to the LTE system while maintaining the connection to thegNB. The term “dual radio” denotes having two RF chains; thus, it ispossible to have data communications via separate RF chainscorresponding to the next generation mobile communication system modemand the LTE modem.

If the UE has a single radio, it may use only one communication modemfor data communication at a time. In order to maintain the connection tothe gNB even in this case, it may be possible to operate in a timedivisional manner The UE with a signal radio may release the connectionto the gNB to perform attach to the LTE system.

If a specific procedure (attach to the target LTE system) is notcompleted before expiry of the timer, it is assumed that thedual-registration procedure has failed. Whether an RRC message includingan attach accept (ATTACH ACCEPT) message is received from a MME 2 b-10determines whether the attach to the target LTE system succeeds.

At step 2 b-26, the UE may directly acquire system information broadcastby the target LTE cell. At step 2 b-28, the UE attempts a random accessto the target LTE cell.

If it fails to either acquire the essential system information of thetarget LTE cell or succeed with the random access after a predeterminednumber of tries, the UE may report the failure to the gNB at step 2b-30. Upon receipt of the failure report, the gNB may trigger aninter-RAT handover or retry the dual registration with another LTEfrequency or cell.

The failure report may include access-failed frequency information orcell ID information and a failure cause. Examples of the failure causemay include system information acquisition failure, random accessfailure, and expiry of the specific timer.

The UE transmits an attach request (ATTACH REQUEST) message to the MMEat step 2 b-34 using a non-access stratum (NAS) container of an RRCConnection Setup Complete message, while performing, at step 2 b-32, anRRC Connection Establishment procedure with the target LTE cell 2 b-06.

The ATTACH REQUEST message includes an indicator indicating that the UEis performing the dual registration to the LTE system. It may also bepossible to further indicate whether the dual registration is requestedfor inter-RAT mobility or inter-RAT aggregation.

If the dual registration is requested for the inter-RAT mobility, thismeans that the UE wants to move from a service area of a source systemto a service area of another system. If the dual registration isrequested for the inter-RAT aggregation, this means that the UE wants toimprove a service throughput performance by establishing an extraconnection to another system.

Upon receipt of the ATTACH REQUEST message including the indicator, theMME performs an S5 session establishment at step 2 b-36 to request tothe Common IP anchor 2 b-12 for routing data to the LTE system ratherthan the next generation system.

In the case of the dual registration for the inter-RAT mobility, theCommon IP anchor changes routings so as to forward all data to thetarget system. In the case of the dual registration for the inter-RATaggregation, the Common IP anchor changes routings such that a part ofthe data is forwarded to the target system while the remaining data arestill being transmitted to the source system.

Upon receipt of the request, the Common IP anchor switches the data flowin whole or in part from the LTE system to the next generation system atstep 2 b-44 and notifies an NG Core 2 b-08 of the data routingconfiguration change at step 2 b-46.

The NG Core notifies the gNB of the change at step 2 b-48 in order forthe gNB to release the connection to the UE. It may also be possible tostop data transfer to implicitly notify the NB Core of the data routingchange. If no data are transmitted from a gateway to the gNB anymore,the gNB may release the connection to the UE after a predetermined timeperiod elapses.

If the ATTACH REQUEST message is successfully received, the MMEtransmits an attach accept (ATTACH ACCEPT) message to the UE at step 2b-38. Upon receipt of this message, the UE assumes that the dualregistration operation is successfully completed.

In this case, the UE stops the timer. Optionally, the UE may notify thegNB, at step 2 b-40, that the dual registration is successfullycompleted using a predetermined message upon receipt of the ATTACHACCEPT message. Upon receipt of this message, the gNB releasesconnection to the UE at step 2 b-42. After the dual registrationprocedure is completed, releasing the connection to the next generationsystem may be performed in an implemental aspect of the UE. All that isrequired for the UE to maintain the connection to the next generationsystem is to generate uplink data.

As in the legacy LTE system, if a radio link failure (RLF) occurs in thenext generation system after the dual registration operation issuccessfully completed, the UE declares RLF and either transmits an RLFreport indicating whether it is dual-registered or makes no RLF reportto the next generation system.

FIG. 2C is a signal flow diagram illustrating signal flows in a casewhere a UE moves from a service area of a next generation mobilecommunication system to a service area of a legacy LTE system accordingto an embodiment of the disclosure.

An eNB 2 c-04 and a UE 2 c-02 located in the service area of the eNB 2c-04 exchange their capability information indicating whether theysupport dual registration at step 2 c-13.

The eNB notifies UEs located within its service area whether the LTEsystem supports dual-registration by broadcasting system information.The UE notifies the eNB whether it supports dual registration via UEcapability information (UECapabilitylnformation) as dedicated signaling.

At step 2 c-14, the eNB configures next generation mobile communication(New Radio (NR)) frequency measurement to the UE. The configurationinformation may include an NR frequency measurement periodicity and atime period for measuring on the NR frequency at the periodicity.

Upon receipt of the configuration information, the UE may performmeasurement on the NR frequency during the measurement period at step 1c-16. The UE may also perform measurement on the NR frequency at anappropriate timing that is autonomously determined. An example of theappropriate timing is a time period during which no data are exchangedwith the eNB.

In order to perform measurement on the NR frequency, the UE turns on anNR modem. If the UE has a dual radio, it may maintain the turn-on stateof the NR modem or turn on and off the NR modem for starting and endingthe measurement at every NR frequency measurement occasion.Alternatively, the UE supporting dual registration may performmeasurement on the NR frequency without any configuration from the eNB.However, in this case, the UE may be able to perform measurement on theNR frequency only at appropriate timings that are autonomouslydetermined by itself.

The UE reports a measurement result to the eNB at step 2 c-18. The eNBdetermines at step 2 c-20 whether to configure dual registration orinter-RAT handover based on the measurement result and otherinformation.

The eNB configures dual registration to the UE at step 2 c-22. For thispurpose, the eNB uses an RRC Connection Reconfiguration(RRCConnectionReconfiguration) message or an RRC Connection Release(RRCConnectionRelease) message.

If the RRCConnectionRelease message is received, this means that the UEreleases the connection to the source cell, and the source celltransmits this message to the UE only when it determines that releasingthe connection to the terminal is preferable.

For example, if the UE has a single radio that cannot establishconnections with two systems simultaneously and does not support anytime division multiplexing scheme for making it possible to establishconnections with two systems, the eNB transmits the RRCConnectionReleasemessage.

If at least one of the above messages is received, the UE performs dualregistration. The above messages may indicate an NR system frequency orcell to which the UE has to attempt to attach to. The above messagesalso provide a list of frequencies or cells in order for the UE toselect one of the frequencies or cells contained in the list and attachthereto. The frequency or cell may be identified with a frequencybandwidth, center frequency information, and a cell ID (Physical cell IDor ECGI).

In order to reduce the time required for the UE to attach, the messagemay include partial system information of an NR system cell 2 c-06. Thepartial system information is essential information for use in accessinga target system. The essential system information may include a list ofPLMNs supported by the NR system cell, a Tracking Area Code, a closedsubscriber group (CSG) cell ID, a list of frequency bands supported by atarget system cell and spectrum emission information, accessbarring-related information (e.g., ACB, EAB, SSAC, and ACDC),configuration information associated with random access to the LTEsystem cell, and cell reselection prioritization information.

The essential system information of the NR system cell may be reportedalong with a cell measurement report according to a request from theeNB, or the eNB may always collect system information of neighboring NRsystem cells from specific UEs with a service area using a SONtechnology.

Upon receipt of the dual-registered initialization message, the UEstarts a predetermined timer at step 2 c-24. If a predeterminedprocedure (procedure for attach to the target NR system) is notcompleted before the timer expires, it is assumed that thedual-registration procedure has failed. Whether an RRC message includingan ATTACH ACCEPT message is received from a NG Core 2 c-10 determineswhether the attach to the target NR system succeeds.

At step 2 c-26, the UE may directly acquire system information broadcastby the target NR cell. At step 2 c-28, the UE attempts a random accessto the target NR cell. If it fails to either acquire the essentialsystem information of the target NR cell or succeed with the randomaccess after a predetermined number of tries, the UE may report thefailure to the eNB at step 2C-30.

Upon receipt of the failure report, the eNB may trigger an inter-RAThandover or retry the dual registration with another NR frequency orcell. The failure report may include access-failed frequency informationor cell ID information and a failure cause. Examples of the failurecause may include system information acquisition failure, random accessfailure, and expiry of the specific timer.

The UE transmits an ATTACH REQUEST message to the NG core at step 2 c-34using a non-access stratum (NAS) container of a specific control planemessage, while performing, at step 2 c-32, an RRC ConnectionEstablishment procedure with the target NR system cell.

The ATTACH REQUEST message includes an indicator indicating that the UEis performing the dual registration to the NR system. Upon receipt ofthe ATTACH REQUEST message including the indicator, the NG Core performsa S5 session establishment at step 2 c-36 to request to the Common IPanchor 2 c-12 for routing data to the NR system rather than the LTEsystem.

Upon receipt of the request, the Common IP anchor switches the data flowin whole or in part from the NR system to the LTE system at step 2 c-44and notifies the MME 2 b-08 of the data routing configuration change atstep 2 c-46.

The MME notifies the eNB of the change at step 2 c-48 in order for theeNB to release the connection to the UE. It may also be possible to stopdata transfer to implicitly notify the NB Core of the data routingchange. If no data are transmitted from a gateway to the eNB anymore,the eNB may release the connection to the UE after a predetermined timeperiod elapses.

If the ATTACH REQUEST message is successfully received, the MMEtransmits an ATTACH ACCEPT message to the UE at step 2 c-38. Uponreceipt of this message, the UE assumes that the dual registrationoperation is successfully completed.

In this case, the UE stops the timer. Optionally, the UE may notify theeNB, at step 2 c-40, that the dual registration is successfullycompleted using a predetermined message upon receipt of the ATTACHACCEPT message. Upon receipt of this message, the gNB releasesconnection to the UE at step 2 c-42.

After the dual registration procedure is completed, releasing theconnection to the NR system may be performed in an implemental aspect ofthe UE. All that is required for the UE to maintain the connection tothe LTE system is to generate uplink data. If an RLF occurs in the LTEsystem after the dual registration operation is successfully completed,the UE declares RLF and either transmits an RLF report indicatingwhether it is dual-registered or makes no RLF report to the nextgeneration system.

FIG. 2D is a flowchart illustrating a procedure for a network todetermine initialization of a dual-registered operation.

A source system determines at step 2 d-02 that a UE needs to establish aconnection with another system based on measurement information reportedby the UE and other information. The source system determines at step 2d-04 whether an interface for interoperating with the other system isimplemented. It is assumed that it is inevitable to have an interfacefor supporting inter-RAT handover, and the interface includes at leastone of an interface between an NG Core and an MME, an interface betweena gNB and the MME, or an interface between the NG Core and an eNB.

If the interface exists, this means that the inter-RAT handover issupported and, in this case, it may be possible to configure thehandover to the UE at step 2 d-10. If the interface does not exist, adual-registration operation should be configured. Even when the sourcesystem has the interface, the dual-registration operation may beconfigured for the purpose of reducing signaling overhead.

The source system determines at step 2 d-06 whether the UE supports thedual radio. The UE transmits corresponding information to the sourcesystem in advance. If the UE has the dual radio, it attempts to attachto a target system at step 2 d-16 while maintaining the connection tothe current system. The reason for maintaining the connection is toavoid any service interruption by continuing to communicate data evenwhile performing the attach procedure.

If the UE has the dual radio, the source system determines at step 2d-08 whether the source system and the UE support a time divisionsolution. The time division solution is a technique for communication ofdata with one system at a time. It may be assumed that the UE supportingthe dual registration must support the time division solution.

If the source system and the UE support the time division solution, theUE maintains the connection to the source system to communicate data ina time divisional manner Data transmission/reception timings of thesource and target systems may be overlapped. In this case, one of thetwo systems performs data communication according to a predeterminedrule. If the source system and the UE do not support the time divisionsolution, the UE releases the connection to the source system andperforms an attach operation at step 2 d-12.

FIG. 2E is a diagram for explaining scenarios where a dual-registered UEis in an idle mode in two respective systems.

In various situation, the dual-registered UE may be in the idle mode inboth the two registered systems. For example, a UE may be connected to anext generation mobile communication system (New Ratio (NR) or New RAT)for receiving a data service. If the terminal moves to a neighboring LTEsystem, the NR system may trigger dual registration of the UE. In thiscase, the UE performs an ATTACH procedure to the LTE system.

Through the ATTACH procedure, the UE registers itself with the LTEsystem. In order to avoid service interruption, the UE may maintain theconnection to the NR system and continue data transmission. If apredetermined time elapses after establishing the connection to the LTEsystem, the UE releases the connection to the NR system. In this case,the UE may transition to the idle mode in the NR system or deregisteritself through a DETACH procedure.

Assuming that the UE transitions to the idle mode, the UE may transitionto the idle mode or deregister itself through the DETACH procedure evenin the LTE system after completing the data communication with the LTEsystem. If the UE transitions to the idle mode in the LTE system too,the UE is in the idle mode in both the two systems.

Transitioning to the idle mode in both the two systems has advantagesand disadvantages. One of the advantages is that the UE can quicklytransition to a connected mode in both the two systems. The network mayselect one of the two systems for delivery of paging based on a servicetype, a UE type (normal UE, machine type communication (MTC) UE, etc.),user subscription, etc. according to an optimization technique.

One of the disadvantages is that the UE has to monitor both the twosystems for delivery of paging. The UE may also have to perform cellmeasurement separately according to system-specific discontinuousreception (DRX) configurations (paging cycle, etc.). This means anincrease of power consumption of the UE.

In this regard, the disclosure proposes a method for saving powerconsumption of a dual-registered UE in the idle mode in both the twosystems.

FIG. 2F is a signal flow diagram for explaining a first solutionaccording to an embodiment of the disclosure.

The first solution is characterized in that a UE or a network selects asystem for delivery of paging such that paging is transmitted by theselected system.

At step 2 f-14, the UE 2 f-02 performs ATTACH to an NR system. Throughthis, the UE is registered with an NG Core 2 f-08. At step 2 f-16, theNG Core establishes a session with a Common IP Anchor 2 f-12 forsupporting the UE. The Common IP Anchor is connected to the NG Core andan MME and transmits the paging to the NG Core or the MME or routesdata. The Common IP Anchor may be called different names in differentstandardized technologies.

At step 2 f-18, the NR system configures dual registration with the LTEsystem to the UE. At step 2 f-20, the UE transmits an ATTACH REQUESTmessage to the MME 2 f-10. The ATTACH REQUEST message (NAS message) mayinclude an ID (RAT id) indicating a system from which the UE wants toreceive the paging.

At step 2 f-22, the MME reports to the Common IP Anchor that the UE hasentered the dual registration mode based on a message including the RATID received from the UE. A session is established between the MME andthe Common IP Anchor for supporting the UE.

The Common IP Anchor determines a system for paging delivery to the UE.In order to make this determination, the Common IP Anchor uses aUE-preferred system, UE type, and user subscription information. Theuser subscription information is provided by a home subscriber server(HSS) and typically includes a user's configuration information (serviceagreement, etc.). The determined system is notified to the NG Core andMME. The NG Core or MME may determine the system and, in this case, itis necessary to notify the Common IP Anchor of the system selected fordelivery of paging.

If the system for delivery of paging is determined, the Common IP Anchornotifies the MME and the NG Core of the determined system, and the MMEor NG Core transmits, at step 2 f-24, to the UE an NAS message includingID information indicating the system determined for delivery of paging.

At step 2 f-26, the UE releases the connection to the NR system andtransitions to the idle mode. At step 2 f-28, the UE releases theconnection to the LTE system and transitions to the idle mode. Thetransition to the idle mode in the two systems may be performed inreverse order or simultaneously. Typically, as the completion of thenecessary data communication is delayed, the transition to the idle modeis delayed.

At step 2 f-30, the UE in the idle mode in both the two systems monitorsonly the system notified by the MME for paging. For example, if the MMEhas notified the UE of the NR system, the UE monitors only the NR systemfor paging.

At step 2 f-32, the UE performs cell measurement according to the DRXcycle of the NR system. Typically, the UE in the idle mode measuresneighboring cells in every DRX cycle for supporting mobility. In thedisclosure, it is characterized that the cells on which the UE performsmeasurement should include the frequency of the LTE cell on which the UEcamped in the LTE system (system not monitored for paging).

At step 2 f-34, the Common IP Anchor recognizes that data to bedelivered to the UE has arrived from a serving gateway (S-GW) (or packetdata network gateway (P-GW).

At step 2 f-36, the Common IP Anchor triggers paging and transmitspaging to the NG Core. The NG Core transmits the paging to the UE viathe gNB 2 f-04. The S-GW (or P-GW) may directly report the arrival ofthe data to the NG Core and the MME. Because the NG Core and the MMEalso know which entity is to deliver the paging to the UE, thecorresponding system may deliver the paging to the UE. In this case, theCommo IP Anchor is not involved.

Although the drawing shows that the MME receives the information on thesystem for delivery of paging from the UE or transmits the informationon the determined system to the UE, the MME may be replaced by the NGCore.

FIG. 2G is a flowchart illustrating operations of a UE in the firstsolution according to an embodiment of the disclosure.

At step 2 g-02, the UE initializes dual registration. The dualregistration may be configured by a network or the UE when apredetermined condition is fulfilled. At step 2 g-04, the UE receivesinformation on the system for delivery of paging through an ATTACH ortracking area update (TAU) procedure. This information is received fromat least one of two systems.

At step 2 g-06, the UE transitions to the idle mode in both the systems.At step 2 g-08, the UE monitors the system indicated by the informationfor paging. At step 2 g-10, the UE performs cell measurement based onDRX configuration information of the system indicated by theinformation. The cell measurement should be performed even on the cellfrequency of the other system in which the UE is in the idle mode. Thisaims to support idle mode mobility effectively in the other system.

FIG. 2H is a flowchart for explaining operations of an NG Core or an MMEin the first solution of the disclosure.

At step 2 h-02, the NG Core or MME receives an ATTACH REQUEST or TAUREQUEST including information on the system for delivery of paging froma UE. An ATTACH procedure is a procedure for registering the UE with theNG Core or MME, and a TAU procedure is a procedure for notifying, whenthe terminal moves out of a tracking area (TA) consisting of one or morecells, the NG Core or MME of the move out of the TA. Upon receipt of theTAU REQUEST, the NG Core or MME notifies the UE of an appropriate TA andafterward transfers paging to the changed TA.

At step 2 h-04, the NG Core or MME transmits dual registration-relatedinformation to the Common IP anchor, the dual registration-relatedinformation including information on the system for delivery of paging.

At step 2 h-06, the NG Core or MME receives the information on thesystem for delivery of paging from the Common IP Anchor. The informationincludes an ID indicative of the system for delivery of paging. Thesystem for delivery of paging may include at least one of an NR systemor an LTE system. A system that is not indicated by the information isassumed to be a system not involving delivery of paging.

At step 2 h-08, the NG Core or MME transmits an ATTCH ACCEPT or TAUACCEPT message including information on the system for delivery ofpaging to the UE. At step 2 h-10, if the NG Core or MME receives paging(or a report indicating that data to be delivered to the UE has arrived)from the S-GW, P-GW, or Common IP Anchor, it determines whether it isthe system for delivery of paging and, if so, delivers the paging (orgenerates and transmits paging) to the UE via the gNB. If it is not thesystem for delivery of paging, the NG Core or MME discards the receivedpaging.

FIG. 21 is a flowchart for explaining operations of a Common IP Anchorin the first solution of the disclosure.

At step 2 1 -02, the Common IP Anchor recognizes that a UE has enteredthe dual registration mode based on information provided by the NG Coreand MME.

At step 2 1 -04, the Common IP Anchor determines one of the NR systemand the LTE system as a system for delivery of paging. In order to makethis determination, the Common IP Anchor uses a UE-preferred system, UEtype, and user subscription information. The user subscriptioninformation is provided by a home subscriber server (HSS) and typicallyincludes a user's configuration information (service agreement, etc.).

At step 2 1 -06, the Common IP Anchor transmits information on thesystem determined for delivery of paging to the NG Core or MME. At step2 1 -08, the Common IP Anchor detects arrival of data to be delivered tothe UE at the S-GW or P-GW and generates pertinent paging. At step 2 1-10, the Common IP Anchor transmits the paging to the NG Core or MME fordelivery of the paging.

FIG. 2J is a signal flow diagram for explaining a second solutionaccording to an embodiment of the disclosure.

The second solution is characterized in that the UE requests for a powersaving mode (PSM) or an extended DRX (eDRX) to a system that is notinvolved in delivery of paging.

If the PSM or eDRX is configured, the UE monitors the PSM- oreDRX-configured system for paging with a very long cycle, therebyavoiding monitoring two systems unnecessarily frequently for paging.

At step 2 j-14, the UE 2 j-02 performs ATTACH to the NR system. Throughthis, the UE is registered with the NG Core 2 j-08.

At step 2 j-16, the NG Core establish a session with the Common IPAnchor 2 j-12 for supporting the UE. The Common IP Anchor is connectedto the NG Core and an MME and transmits the paging to the NG Core or theMME or routes data. The Common IP Anchor may be called different namesin different standardized technologies.

At step 2 j-18, the NR system configures dual registration with the LTEsystem to the UE. At step 2 j-20, the UE transmits an ATTACH REQUESTmessage to the MME 2 j-10. At step 2 j-22, the MME reports to the CommonIP Anchor that the UE has entered the dual registration mode. A sessionis established between the MME and the Common IP Anchor for supportingthe UE.

At step 2 j-24, the MME or NG Core transmits an NAS message to the UE.At step 2 j-26, the UE releases the connection to the NR system andtransitions to the idle mode. At step 2 j-28, if the UE does not want toreceive any paging from the LTE system, it requests to the LTE systemfor the PSM or eDRX. This request is made through an ATTACH or TAUprocedure.

At step 2 j-30, the UE receives PSM or eDRX configuration informationfrom the MME. The UE performs a PSM or eDRX operation based on thisconfiguration information. Although the description is directed to thecase where the PSM or eDRX is applied to the LTE system in thedisclosure, it may also be possible to apply the PSM or eDRX to the NRsystem instead of the LTE system in the same manner.

At step 2 j-32, the UE releases the connection to the LTE system andtransitions to the idle mode. The transition to the idle mode in the twosystems may be performed in reverse order or simultaneously. Typically,as the completion of the necessary data communication is delayed, thetransition to the idle mode is delayed.

At step 2 j-34, the UE is in the idle mode in both the two systems andperforms monitoring for paging in consideration of the PSM or eDRXconfiguration. Typically, if the PSM or eDRX is configured, pagingmonitoring is performed with a very long cycle, which reduces powerconsumption of the UE.

At step 2 j-36, the UE performs cell measurement according tosystem-specific DRX cycles. The UE in the idle mode measures theneighboring cells in every DRX cycle for supporting mobility. Forexample, if the PSM or eDRX is configured, paging monitoring isperformed with a very long cycle, and the UE can reduce powerconsumption. In the disclosure, it is characterized that the cells onwhich the UE performs measurement should include the frequency of theLTE cell on which the UE camped in the LTE system (system to which thePSM or eDRX has been applied).

At step 2 j-38, the MME notifies the Common IP Anchor that the UE isconfigured with the PSM or eDRX in the LTE system. At step 2 j-40, theCommon IP Anchor recognizes that data to be delivered to the UE hasarrived from the S-GW (or P-GW).

At step 2 j-47, the Common IP Anchor triggers paging and transmitspaging to the NG Core. The NG Core transmits the paging to the UE viathe gNB 2 j-04. The S-GW (or P-GW) may directly report the arrival ofthe data to the NG Core and the MME.

Depending on whether the PSM or eDRX has been applied, the NG Core andMME of the corresponding system may deliver the paging to the UE. Inthis case, the Common IP Anchor is not involved. The UE may receivepaging from the system to which the PSM or eDRX has been applied. The UEmay also receive the same paging from the other system. If the UEreceives the paging from the two systems simultaneously, the UE mayoperate according to the paging from the system to which the PSM or eDRXhas not been applied.

Although the drawing shows that the MME receives the information on thesystem for delivery of paging from the UE or transmits the informationon the determined system to the UE, the MME may be replaced by the NGCore.

FIG. 2K is a signal flow diagram for explaining a power saving mode(PSM).

At step 2 k-25, a UE 2 k-00 supporting PSM requests to an MME 2 k-15 ofa network for PSM. This request is made when the UE performs ATTACH orTAU with the MME. ATTACH means a procedure for the UE to register itselfwith the MME.

The MME provides the UE with Registered PLMN and Equivalent PLMNinformation through the ATTACH procedure. The TAU procedure is performedfor the UE to notify the network of its location. In the LTE standardtechnology, the network locates a UE by a TA for paging. A TA is a groupof one or more cells. If a UE on the move enters a different TA, the UEnotifies the network that it has entered a new TA. In order to performthe ATTACH and TAU procedures, it is necessary to communicate with anMME and this means that the UE has to transition from the idle mode tothe connected mode at step 2 k-20.

At step 2 k-30, the MME accepts the PSM request from the UE and providesthe UE two kinds of timer values. One is an active timer and the otheris a periodic TAU timer. The two timers start at steps 2 k-40 and 2 k-45upon transition from the connected mode to the idle mode at step 2 k-35.Simultaneously, the MME starts a timer at step 2 k-50.

The UE operates in the idle mode until the active timer expires. If theactive timer expires, the UE enters, at step 2 k-65, the PSM, in which,at step 2 k-60, all idle mode operations and AS timers stop. If theperiodic TAU timer expires at step 2 k-70 or a mobile originating (MO)call is triggered at step 2 k-75, the UE wakes up from PSM and entersthe idle mode to perform idle mode operations at step 2 k-80. If the UEwants to trigger PSM again, it has to request to the MME for PSM at step2 k-85.

The eDRX is newly employed in the LTE Rel-13 standard. The eDRX aims tomonitor a physical downlink control channel (PDCCH) for paging with acycle longer than the legacy DRX cycle. The eDRX specified in the LTEstandard document TS36.304 is as follows.

7.3 Paging in Extended DRX

The UE may be configured by upper layers with an extended DRX (eDRX)cycle T_(eDRX). The UE may operate in extended DRX only if the cellindicates support for eDRX in System Information.

If the UE is configured with a T_(eDRX) cycle of 512 radio frames, itmonitors POs as defined in 7.1 with parameter T=512. Otherwise, a UEconfigured with eDRX monitors POs as defined in 7.1 (i.e., based on theupper layer configured DRX value and a default DRX value determined in7.1), during a periodic Paging Time Window (PTW) configured for the UEor until a paging message including the UE's NAS identity is receivedfor the UE during the PTW, whichever is earlier. The PTW is UE-specificand is determined by a Paging Hyperframe (PH), a starting positionwithin the PH (PTW start), and an ending position (PTW_end). PH, PTWstart, and PTW_end are given by the following formulae.

The PH is the H-SFN satisfying the following equation:

H-SFN mod T_(eDRX,H)=(UE_ID_H mod T_(eDRX,H)),

UE_ID_H:

-   -   10 MSB (most significant bits) of the Hashed ID, if P-RNTI is        monitored on PDCCH or MPDCCH    -   12 MSB (most significant bits) of the Hashed ID, if P-RNTI is        monitored on NPDCCH

IMSI mod 1024

T_(eDRX,H): eDRX cycle of the UE in Hyper-frames, (T_(eDRX,H)=1, 2, . .. , 256 Hyper-frames) (for NB-IoT, T_(eDRX,H)=2, . . . , 1024Hyper-frames) and configured by upper layers.

PTW start denotes the first radio frame of the PH that is part of thePTW and has SFN satisfying the following equation:

SFN=256* i _(cDRX), where

-   -   i_(eDRX)=floor(UE_ID_H/T_(eDRX,H)) mod 4

PTW_end is the last radio frame of the PTW and has SFN satisfying thefollowing equation:

SFN=(PTW_start+L*100−1)mod 1024, where

-   -   L=Paging Time Window length (in seconds) configured by upper        layers

Hashed ID is defined as follows:

Hashed_ID is Frame Check Sequence (FCS) for the bits b31, b30 . . . , b0of S-TMSI, computed according to 32-bit FCS defined in Section 8.1.1.6.2of [34], and S-TMSI=<b39, b38, . . . , b0> as defined in [35].

In the eDRX technique, the UE transmits UE-preferred eDRX cycleinformation to the MME through the ATTACH or TAU procedure. The MMEconfigures eDRX to the UE.

FIG. 2L is a flowchart for explaining operations of a UE in the secondsolution of an embodiment of the disclosure.

At step 2 l-02, the UE initializes dual registration. The dualregistration may be configured by a network or the UE when apredetermined condition is fulfilled.

At step 2 l-04, the UE requests for PSM or eDRX configuration to atleast one of two systems through an ATTACH or TAU procedure. At step 2l-06, the UE receives PSM or eDRX configuration from the NG Core or theMME and initializes the PSM or eDRX. At step 2 1 -08, the UE transitionsto the idle mode in both the two systems.

At step 2 l-10, the UE monitors the two system for paging. However, thesystem configured with the PSM or eDRX is monitored with a very longcycle. This is because the UE stops all idle mode operations during thePSM cycle or stops monitoring for paging during the inactive time of thevery long eDRX cycle.

At step 2 l-12, the UE performs cell measurement based on the DRXconfiguration information of the system indicated by the information.The cell measurement should be performed even on the cell frequency ofthe other system in which the UE is in the idle mode. This aims tosupport idle mode mobility effectively in the other system.

FIG. 2M is a flowchart for explaining operations of an NG Core or an MMEin the second solution of the disclosure.

At step 2 m-02, the NG Core or MME receives an ATTACH REQUEST or TAUREQUEST including PSM or eDRX request information from the UE. An ATTACHprocedure is a procedure for registering the UE with the NG Core or MME,and a TAU procedure is a procedure for notifying, when the terminalmoves out of a tracking area (TA) consisting of one or more cells, theNG Core or MME of the move out of the TA. Upon receipt of the TAUREQUEST, the NG Core or MME notifies the UE of an appropriate TA andafterward transfers paging to the changed TA.

At step 2 m-04, the NG Core or MME transmits PSM or eDRXconfiguration-related information to the Common IP Anchor. At step 2m-06, the NG Core or MME transmits the PSM or eDRX configuration to theUE.

FIG. 2N is a flowchart illustrating operations of a Common IP Anchor inthe second solution of the disclosure.

At step 2 n-02, the Common IP Anchor recognizes that a UE has enteredthe dual registration mode based on the information provided by the NGCore and MME. At step 2 n-04, the Common IP Anchor ascertains that theUE applies PSM or eDRX to one of the NR and LTE systems based on areport from the two systems.

At step 2 n-06, the Common IP Anchor generates, upon arrival of data tobe delivered to the UE from the S-GW or P-GW, pertinent paging. At step2 n-08, the Common IP Anchor transmits the paging to the NG Core or MMEfor delivery of the paging. The system with which the PSM or eDRX isconfigured is excluded because it cannot deliver the paging.

FIG. 20 is a block diagram illustrating a configuration of a UEaccording to an embodiment of the disclosure.

In reference to FIG. 20, the UE includes a radio frequency (RF)processing unit 2 o-10, a baseband processing unit 2 o-20, a memory 2o-30, and a controller 2 o-40.

The RF processing unit 2 o-10 takes charge of signal band conversion andamplification for transmitting signals over a radio channel. That is,the RF processing unit 2 o-10 up-converts a baseband signal output fromthe baseband processing unit 2 o-20 to an RF band signal fortransmission through antennas and down-converts an RF band signalreceived through an antenna to a baseband signal.

For example, the RF processing unit 2 o-10 may include a transmissionfilter, a reception filter, an amplifier, a mixer, an oscillator, adigital-to-analog converter (DAC), and an analog-to-digital convertor(ADC). Although one antenna is depicted in the drawing, the terminal mayinclude a plurality of antennas.

The RF processing unit 2 o-10 may include a plurality of RF chains. TheRF processing unit 2 o-10 may perform beamforming For beamforming, theRF processing unit 2 o-10 may adjust the phases and sizes of the signaltransmitted/received through the antennas or antenna elements. The RFprocessing unit 2 o-10 may perform a MIMO operation to receive a signalon multiple layers.

The baseband processing unit 2 o-20 takes charge of conversion betweenbaseband signals and bit strings according to a physical layer protocolof the system. For example, the baseband processing unit 2 o-20 performsencoding and modulation on the transmit bit strings to generate complexsymbols in data transmission mode.

The baseband processing unit 2 o-20 also performs demodulation anddecoding on the baseband signal from the RF processing unit 2 o-10 torecover the received bit strings in data reception mode. For the case ofan orthogonal frequency division multiplexing (OFDM) system, thebaseband processing unit 2 o-20 performs encoding and modulation on atransmit bit string to generate complex symbols, maps the complexsymbols to subcarriers, performs inverse fast Fourier transform (IFFT)on the subcarriers, and inserts a cyclic prefix (CP) to generate OFDMsymbols in the data transmission mode.

The baseband processing unit 2 o-20 splits the baseband signal from theRF processing unit 2 o-10 into OFDM symbols, recovers the signals mappedto the subcarriers through fast Fourier transform (FFT), and performsdemodulation and decoding to recover the bit strings in the datareception mode.

The baseband processing unit 2 o-20 and the RF processing unit 2 o-10take charge of transmitting and receiving signals as described above.Accordingly, the baseband processing unit 2 o-20 and the RF processingunit 2 o-10 may be referred to as a transmission unit, a reception unit,a transceiver, or a communication unit. At least one of the basebandprocessing unit 2 o-20 and the RF processing unit 2 o-10 may include aplurality of communication modules for supporting different radio accesstechnologies.

At least one of the baseband processing unit 2 o-20 and the RFprocessing unit 2 o-10 may include a plurality of communication modulesfor processing different frequency band signals. Examples of the radioaccess technologies include WLAN (e.g., IEEE 802.11) and cellularnetwork (e.g., LTE). Examples of the different frequency bands mayinclude super high frequency (SHF) band (e.g., 2.5 GHz and 5 GHz) andmillimeter wave (mmWave) bands (e.g., 60 GHz).

The memory 2 o-30 stores basic programs for operation of the terminal,application programs, and data such as configuration information. Inparticular, the memory 2 o-30 may store information related to a secondaccess node that performs radio communication using a second radioaccess technology. The memory 2 o-30 provides the stored data inresponse to a request from the controller 2 o-40.

The controller 2 o-40 controls overall operations of the terminal. Forexample, the controller 2 o-40 controls the baseband processing unit 2o-20 and the RF processing unit 2 o-10 to transmit/receive signals. Thecontroller 2 o-40 also writes and reads data to and from the memory 2o-30. In order to accomplish this, the controller 2 o-40 may include atleast one processor. For example, the controller 2 o-40 may include acommunication processor (CP) for controlling communication and anapplication processor (AP) for providing higher layer processing, e.g.,application layer protocol processing.

FIG. 2P is a block diagram illustrating a configuration of a basestation according to an embodiment of the disclosure.

As shown in the drawing, the base station includes an RF processing unit2 p-10, a baseband processing unit 2 p-20, a backhaul communication unit2 p-30, a memory 2 p-40, and a controller 2 p-50.

The RF processing unit 2 p-10 takes charge of signal band conversion andamplification for transmitting signals over a radio channel. That is,the RF processing unit 2 p-10 up-converts a baseband signal output fromthe baseband processing unit 2 p-20 to an RF band signal fortransmission through antennas and down-converts an RF band signalreceived through the antennas to a baseband signal.

For example, the RF processing unit 2 p-10 may include a transmissionfilter, a reception filter, an amplifier, a mixer, an oscillator, a DAC,and an ADC. Although one antenna is depicted in FIG. 2P, the basestation may include a plurality of antennas. The RF processing unit 2p-10 may include a plurality of RF chains. The RF processing unit 2 p-10may perform beamforming For beamforming, the RF processing unit 2 p-10may adjust the phases and sizes of the signal transmitted/receivedthrough the antennas or antenna elements. The RF processing unit 2 p-10may perform a downlink MIMO operation to transmit a signal on multiplelayers.

The baseband processing unit 2 p-20 takes charge of converting betweenbaseband signals and bit strings according to a physical layer protocolof a first radio access technology. For example, the baseband processingunit 2 p-20 performs encoding and modulation on the transmit bit stringsto generate complex symbols in data transmission mode.

The baseband processing unit 2 p-20 also performs demodulation anddecoding on the baseband signal from the RF processing unit 2 p-10 torecover the received bit strings in data reception mode. For the case ofan OFDM system, the baseband processing unit 2 p-20 performs encodingand modulation on the a transmit bit string to generate complex symbols,maps the complex symbols to subcarriers, performs IFFT on thesubcarriers, and inserts a CP to generate OFDM symbols in the datatransmission mode.

The baseband processing unit 2 p-20 splits the baseband signal from theRF processing unit 2 p-10 into OFDM symbols, recovers the signals mappedto the subcarriers through FFT, and performs demodulation and decodingto recover the bit strings in the data reception mode. The basebandprocessing unit 2 p-20 and the RF processing unit 2 p-10 take charge oftransmitting and receiving signals as described above. Accordingly, thebaseband processing unit 2 p-20 and the RF processing unit 2 p-10 may bereferred to as a transmission unit, a reception unit, a transceiver, ora communication unit.

The backhaul communication unit 2 p-30 provides an interface forcommunication with other network nodes. That is, the backhaulcommunication unit 2 p-30 converts a bit string transmitted from amaster base station to another node, e.g., secondary base station andcore network, to a physical signal and converts a physical signalreceived from another node to a bit string.

The memory 2 p-40 stores basic programs for operation of the basestation, application programs, and data such as configurationinformation. In particular, the memory 2 p-40 may store the informationon the bearers allocated to the connected terminal and a measurementresult reported by the terminal. The memory 2 p-40 may also store theinformation as criteria for determining whether to enable or disablemulti-connectivity for the terminal The memory 2 p-40 provides thestored data in response to a request from the controller 2 p-50.

The controller 2 p-50 may control overall operations of the basestation. For example, the controller 2 p-50 controls the basebandprocessing unit 2 p-20, the RF processing unit 2 p-10, and the backhaulcommunication unit 2 p-30 for transmitting/receiving signals. Thecontroller 2 p-50 also writes and reads data to and from the memory 2p-40. In order to accomplish this, the controller 2 p-50 may include atleast one processor.

The Third Embodiment

The terms used in the following description for indicating access nodes,network entities, messages, interfaces between network entities, anddiverse identity informations are provided for convenience ofexplanation. Accordingly, the terms used in the following descriptionare not limited to specific meanings, and they may be replaced by otherterms equivalent in technical meanings.

In the following description, the terms and definitions given in the 3rdGeneration Partnership Project Long Term Evolution (3GPP LTE) standardare used. However, the disclosure is not limited by the terms anddefinitions, and it can be applied to other standard communicationsystems.

FIG. 3A is a diagram illustrating an architecture of a legacy LTEsystem.

In reference to FIG. 3A, the radio communication system includes evolvedNode Bs (eNBs) 3 a-05, 3 a-10, 3 a-15, and 3 a-20; a Mobility ManagementEntity (MME) 3 a-25; and a Serving Gateway (S-GW) 3 a-30. The UserEquipment (UE or terminal) 3 a-35 connects to an external network viathe eNBs 3 a-05, 3 a-10, 3 a-15, and 3 a-20 and the S-GW 3 a-30.

The eNBs 3 a-05, 3 a-10, 3 a-15, and 3 a-20 access nodes of a cellularnetwork to provide network access service to UEs camped thereon. Thatis, the eNBs 3 a-05, 3 a-10, 3 a-15, and 3 a-20 schedule the UEs basedon buffer status, power headroom status, and channel status collectedfrom the UEs to connect the UEs to the Core Network (CN). The MME 3 a-25is an entity taking charge of UE mobility management and other controlfunctions and maintains connections with a plurality of eNBs, and theS-GW 3 a-30 is an entity for handling bearers. The MME 3 a-25 and theS-GW 3 a-30 may perform authentication on the UEs connected to thenetwork, manage bearers, and process the packets from the eNBs 3 a-05, 3a-10, 3 a-15, and 3 a-20 or to be transmitted to the eNBs 3 a-05, 3a-10, 3 a-15, and 3 a-20.

FIG. 3B is a diagram illustrating a protocol stack in an LTE system.

In reference to FIG. 3B, the protocol stack of the interface between theUE and the eNB in the LTE system includes a packet data convergencecontrol (PDCP) layer denoted by reference numbers 3 b-05 and 3 b-40,radio link control (RLC) layer denoted by reference numbers 3 b-10 and 3b-35, and a medium access control (MAC) layer denoted by referencenumbers 3 b-15 and 3 b-30. The PDCP layer denoted by reference numbers 1b-05 and 1 b-40 takes charge of compressing/decompressing an IP header.The main functions of the PDCP layer can be summarized as follows.

-   -   Header compression and decompression: ROHC only    -   Transfer of user data

In-sequence delivery of upper layer PDUs at PDCP re-establishmentprocedure for RLC AM

-   -   For split bearers in DC (only support for RLC AM): PDCP PDU        routing for transmission and PDCP PDU reordering for reception    -   Duplicate detection of lower layer SDUs at PDCP re-establishment        procedure for RLC AM    -   Retransmission of PDCP SDUs at handover and, for split bearers        in DC, of PDCP PDUs at PDCP data-recovery procedure, for RLC AM    -   Ciphering and deciphering    -   Timer-based SDU discard in uplink

The RLC layer designated by reference numbers 3 b-10 and 3 b-35 takescharge of reformatting PDCP PDUs in order to fit them into the size forARQ operation. The main functions of the RLC layer can be summarized asfollows.

-   -   Transfer of upper layer PDUs    -   Error Correction through ARQ (only for AM data transfer)    -   Concatenation, segmentation, and reassembly of RLC SDUs (only        for UM and AM data transfer)    -   Re-segmentation of RLC data PDUs (only for AM data transfer)    -   Reordering of RLC data PDUs (only for UM and AM data transfer)    -   Duplicate detection (only for UM and AM data transfer)    -   Protocol error detection (only for AM data transfer)    -   RLC SDU discard (only for UM and AM data transfer)    -   RLC re-establishment

The MAC layer denoted by reference numbers 3 b-15 and 3 b-30 allows forconnection of multiple RLC entities established for one UE and takescharge of multiplexing RLC PDUs from the RLC layer into a MAC PDU anddemultiplexing a MAC PDU into RLC PDUs. The main functions of the MAClayer can be summarized as follows.

-   -   Mapping between logical channels and transport channels    -   Multiplexing/demultiplexing of MAC SDUs belonging to one or        different logical channels into/from transport blocks (TB)        delivered to/from the physical layer on transport channels    -   Scheduling information reporting    -   Error correction through HARQ    -   Priority handling between logical channels of one UE    -   Priority handling between UEs by means of dynamic scheduling    -   MBMS service identification    -   Transport format selection    -   Padding

The physical layer denoted by reference numbers 3 b-20 and 3 b-25 takescharge of channel-coding and modulation on higher layer data to generateand transmit OFDM symbols over a radio channel, and demodulating andchannel-decoding on OFDM symbols received over the radio channel todeliver the decoded data to the higher layers.

Although not shown in the drawing, there is a radio resource control(RRC) layer above the PDCP layer that is responsible for exchangingaccess and measurement-related configuration control messages betweenthe UE and the base station.

FIG. 3C is a schematic diagram illustrating a dual-connectivityoperation in a legacy LTE system.

In reference to FIG. 3C, in the case where eNB 1 3 c-05 uses a carrierwith a center frequency f1 for communication and an eNB 2 3 c-15 uses acarrier with a center frequency f2 for communication, a UE 3 c-01 mayaggregate the carrier with the downlink center frequency f1 and thecarrier with the downlink center frequency f2 to communicate with two ormore eNBs. The LTE system supports such an operation, which is calledDual Connectivity (hereinafter, referred to as DC).

In the following description, if a UE receives data through a certaindownlink carrier or transmits data through a certain uplink carrier,this means to receive or transmit data through a control channel and adata channel provided in a cell corresponding to a center frequency anda frequency band characterizing the carrier.

In the following description, a set of the serving cells controlled byone eNB is referred to as a Cell Group or Carrier Group (CG). A cellgroup is classified into one of Master Cell Group (MCG) and SecondaryCell Group (SCG). The MCG denotes a set of the serving cell controlledby an eNB controlling the PCell (hereinafter, referred to as Master eNB(MeNB)), and the SCG denotes a set of the serving cells controlled bythe eNB that does not control the PCell, i.e., the eNB that controlsonly SCells (hereinafter, referred to as Slave eNB (SeNB)). The eNBnotifies the UE whether a serving cell belongs to the MCG or SCG in theprocedure of configuring the corresponding serving cell.

The PCell and SCell are terms expressing the types of the serving cellconfigured to the UE. The PCell and SCell are different in that thePCell always remains in the activated state while the SCell transitionsbetween the activated state and the deactivated state repeatedlyaccording to the command of the eNB. The UE mobility is controlledmainly in association with the PCell, and the SCell may be understood asan extra serving cell for data communication. In the followingdescription, the meanings of the terms “PCell” and “SCell” are the sameas those defined in the LTE standards TS36.331 and TS 36.321.

In FIG. 3C, if eNB 1 3 c-05 is an MeNB and eNB 2 3 c-15 is an SeNB, aserving cell 3 c-10 with the center frequency f1 is a serving cellbelonging to an MCG, and a serving cell 3 c-20 with the center frequencyf2 is a serving cell belonging to an SCG.

Meanwhile, it may be practically impossible to transmit hybrid automaticrepeat request (HARQ) feedbacks and channel status information (CSI) forSCG S Cells through a physical uplink control channel (PUCCH) of aPCell. This is because a transmission delay between the MeNB and SeNBmay be longer than the HARQ RTT (typically, 8 ms) within which an HARQfeedback should be delivered. For this reason, one of the SCellsbelonging to the SCG is configured as a primary SCell (PSCell) withPDCCH transmission resources for transmitting HARQ feedback and CSIs forthe SCG SCells.

FIG. 3D is a diagram illustrating a next generation mobile communicationsystem architecture to which the disclosure is applied.

As shown in FIG. 3D, the next generation mobile communication systemincludes a radio access network with a next generation base station (NewRadio Node B (NR gNB) or NR base station) 3 d-10 and a new radio corenetwork (NR CN) 3 d-05. A new radio user equipment (NR UE or NRterminal) 3 d-15 connects to an external network via the NR gNB 3 d-10and the NR CN 3 d-05.

In FIG. 3D, the NR gNB 3 d-10 corresponds to an evolved Node B (eNB) ofthe legacy LTE. The NR gNB 3 d-10 to which the NR UE 3 d-15 connectsthrough a radio channel is capable of providing superior services incomparison with the legacy eNB. In the next generation mobilecommunication system where all user traffic is served through sharedchannels, it is necessary to schedule the NR UEs based on schedulinginformation such as buffer status, power headroom status, and channelstatus collected by the NR UEs, and the NR gNB 3 d-10 takes charge ofthis function.

Typically, the NR gNB 3 d-10 controls multiple cells and includes acentral unit (CU) responsible for control and signaling and adistributed unit (DU) responsible for signal communication. In order toachieve a data rate higher than the peak data rate of legacy LTEsystems, the next generation mobile communication system may adopt abeamforming technique along with orthogonal frequency divisionmultiplexing (OFDM) as a radio access technology. The NR gNB may alsoadopt an adaptive modulation and coding (AMC) to determine themodulation scheme and channel coding rate in adaptation to the channelcondition of the NR UE.

The NR CN 3 d-05 takes charge of mobility support, bearer setup, and QoSconfiguration. The NR CN 3 d-05 may take charge of an NR UE mobilitymanagement function, and a plurality of NR gNBs may connect to the NR CN3 d-05. The next generation mobile communication system may alsointeroperate with a legacy LTE system and, in this case, the NR CN 3d-05 connects to an MME 3 d-25 through a network interface. The MME 3d-25 communicates with at least one eNB 3 d-30 as a legacy base station.

FIG. 3E is a signal flow diagram illustrating a handover procedure in anLTE system for reference to explain the disclosure.

At step 3 e-05, a UE 3 e-01 in a connected mode transmits cellmeasurement information (Measurement Report) to a serving eNB 3 e-02periodically or when a predetermined event occurs. The serving eNBdetermines whether to hand the UE over to a neighboring cell based onthe measurement information. The handover is a technique for switchingfrom a serving cell serving a UE to another eNB.

If the serving cell makes a handover decision, it transmits a handover(HO) request message, at step 3 e-10, to a new eNB, i.e., target eNB 3e-03, to request for handover to continue providing a service. If thetarget cell accepts the handover request, it transmits a HO requestacknowledgement (Ack) message to the serving cell at step 3 e-15.

Upon receipt of this message, the serving cell transmits a HO command tothe UE at step 3 e-20. Before receiving the HO command, the UE continuesreceiving downlink channels (PDCCH/PDSCH/PHICH) from the serving celland transmitting uplink channels (PUSCH/PUCCH). The HO command messageis conveyed in an RRC Connection Reconfiguration message beingtransmitted from the serving cell to the UE at step 3 e-20.

Upon receipt of this message, the UE stops data communication with theserving cell and starts a timer T304. The timer T304 aims for the UE torevert the previous configuration and transitions to an RRC idle stateif it fails to hand the UE over to the target cell during apredetermined time period. The serving cell transmits sequence number(SN) status information for uplink/downlink data to the target eNB and,if any downlink data exists, the data to the target eNB at steps 3 e-30and 3 e-35.

At step 3 e-40, the UE attempts random access to the target cellindicated by the serving cell. The random access is performed to notifythe target cell of the handover of the UE and acquire uplinksynchronization. For the random access, the UE transmits a preambleidentified by a preamble ID provided by the serving cell or selectedrandomly to the target cell.

After a predetermined number of subframes since the transmission of thepreamble, the UE starts monitoring the target cell for a random accessresponse (RAR). A time period for this monitoring is referred to as RARwindow.

If the RAR is received at step 3 e-45 during the RAR window, the UEtransmits, at step 3 e-55, to the target cell an RRC ConnectionReconfiguration Complete (RRCConnectionReconfigurationComplete) messageincluding a HO complete message. Afterward, the UE receives downlinkchannels (PDCCH/PDSCH/PHICH) from the target cell and transmits uplinkchannels (PUSCH/PUCCH) to the target cell. If the RAR is successfullyreceived as described above, the UE ends the timer T304.

The target cell requests for path switching at steps 3 e-60 and 3 e-65to modify the paths of the bearers configured to the serving cell andrequests, at step 3 e-70, to the serving cell to release the UE contextof the UE. The UE attempts to receive data from the target cell at thestart time of the RAR window and starts transmission along withtransmitting an RRC ConnectionReconfigurationComplete message uponreceipt of the RAR.

In the above-described legacy LTE handover, an interruption occursduring the random access procedure to the target cell, which demands arequirement of interference-free mobility management (zero mobilityinterruption time) to avoid interrupting in NR. In the disclosure, thelegacy LTE handover is referred to as Type 1 handover for distinctionfrom the proposed method (hereinafter, referred to as Type 2 handover).

In the disclosure, a target PCell to which a handover is to be performedis a serving cell configured to the UE, and a handover between servingcells is defined as Type 2 handover. The Type 2 handover may be definedas inter-serving cell PCell switching.

1. A PUCCH connection should be configured to one or more serving cellsas well as the PCell. This is because there is a need of an uplinkcontrol channel for transmitting HARQ feedback, scheduling requests, andCSI.

2. A split bearer should be reconfigured for all resource blocks (SRB1,SRB2, and DRBs (Data Radio Bearers) except for SRB 0 (Service RadioBearer 0) before performing the Type 2 Handover.

Typically, the Type 2 handover consists of 4 phases.

1. Phase 0: The UE is connected to the PCell.

2. Phase 1 (preparatory phase): Additional PUCCH serving cell(s) is(are)configured.

3. Phase 2 (execution phase): The Type 2 handover is executed toswitching the PCell to a target serving cell. Here, the serving cellshould be not the PCell but a serving cell configured with a PUCCH.

4. Phase 3 (wrap-up phase): The old PCell is released.

Examples of the Type 2 handover include a dual connectivity- (DC-) andRLC split bearer-based handover, a DC- and MAC split bearer-basedhandover, and enhanced CA-based (eCA-based) handover. In the disclosure,descriptions are directed to the DC- and RLC split bearer-based handoverprocedure. In particular, embodiment 3-1 is directed to inter-gNBmobility, i.e., a handover procedure between two different gNBs, andembodiment 3-2 is directed to an intra-gNB mobility, i.e., a handoverprocedure between cells of the same gNB.

FIGS. 3FA and 3FB are schematic diagrams for explaining a DC- and RLCsplit bearer-based inter-gNB handover operation and a protocol structureaccording to embodiment 3-1 of the disclosure.

In Phase 0, a UE is connected to gNB 1 for basic data communication inthe NR system as denoted by reference number 3 f-05. In the disclosure,it is assumed that the gNB 1 hosts a PCell and an SCell for convenienceof explanation.

In this phase, the gNB 1 configures an MCG bearer for data communicationonly through a serving cell of an MeNB, and each PDCP entity isconnected to one RLC, which is connected to a MAC entity via a logicalchannel as denoted by reference number 3 f-10. The UE configures PDCP,RLC, and MAC according to the bearer configuration with the gNB 1 andreceives a control signal and data through the PCell (Cell1). The UEalso transmits HARQ feedback, scheduling requests, and CSI through thePCell (Cell1) and performs data communication through the SCell (Cell2).The SCell transitions between an activated state and a deactivated staterepeatedly under the control of the gNB 1 as denoted by reference number3 f-15.

If the gNB 1 makes a dual connectivity determination for a handover uponfulfilment of a predetermined condition, dual connectivity is configuredin Phase 1 as denoted by reference number 3 f-20. Next, the gNB 1requests to the gNB 2 for SeNB addition and PDCP and split bearerconfiguration and configures PDCP, RLC, and MAC according to the bearerconfiguration. That is, the gNB 1 establishes dual connectivity with thegNB 2 hosting a PSCell (Cell3) as an additional PUCCH serving cell andan SCell (Cell4) and reconfigures the old MCG bearer into a split beareras denoted by reference numbers 3 f-25 and 3 f-30. This means that eachPDCP entity of the gNB 1 is split to establish links to two RLC entitiesfor the gNB 1 and gNB 2.

As the dual connectivity is established, the UE establishes additionalRLC entities and resets a new MAC entity for the gNB 2 while maintainingthe RLC and MAC configurations of the gNB 1 as denoted by referencenumber 3 f-35.

If the gNB 1 detects an event triggering a handover from a measurementreport value of the UE, e.g., if a signal strength from the gNB 1becomes equal to or greater than a signal strength from the gNB 2, thisleads to Phase 2 in which the roles are switched between the PCell andthe PSCell as denoted by reference number 3 f-40. In this phase, thesplit bearer is reconfigured into another split bearer, S1-U is switchedfrom the gNB 1 to the gNB 2, and the PDCP is relocated as denoted byreference numbers 3 f-45 and 3 f-50. As a consequence, the PDCP of thegNB 1 is released, and the roles of the PCell and PSCell are switched.In the UE, there is little change in Phase 1 with the exception that aprevious configuration of a power headroom report (PHR) is cancelled andlocations of PHs are adjusted in the PHR according to the role switchingof the PCell and the PSCell.

If the gNB 2 detects an event triggering dual connectivity release ofthe gNB 1 from a measurement report value of the UE, e.g., if the signalstrength from the gNB 1 becomes equal to or less than a predeterminedthreshold value, this leads to Phase 3 in which the dual connectivity isreleased as denoted by reference number 3 f-60.

In this phase, the split bearer is reconfigured into an MCB bearer asdenoted by reference number 3 f-65, and the bearer configuration of thegNB 1 is released according to an SCG release request as denoted byreference number 3 f-70. Likewise, the UE releases the RLC and MAC andperforms data communication with the newly configured gNB 2 as denotedby reference number 3 f-75.

FIGS. 3GA and 3GB are signal flow diagrams illustrating a DC- and RLCsplit bearer-based handover procedure according to embodiment 3-1 of thedisclosure.

A description is made of the per-phase signal flows in the DC- and RLCsplit bearer-based inter-gNB handover procedure in detail with referenceto FIGS. 3GA and 3GB.

It is assumed that a UE 3 g-01 in the state of being connected to asource gNB 3 g-02 receives a downlink control signal (PDCCH) and data(PDSCH) at step 3 g-05 and transmits an uplink signal (PUCCH) and data(PUSCH) in Phase 0. In this phase, it may be possible to receive thedownlink control signal and transmit the uplink control signal throughthe PCell of the source gNB and perform further datatransmission/reception through an SCell under the control of the gNB.

The UE measures neighboring cells periodically or as configured by thegNB and, if a predetermined condition is fulfilled, it transmits to thesource gNB, at step 3 g-15, a measurement value (MeasResult) indicatingthe necessity of dual connectivity for a handover, which leads to Phase1. The measurement value may indicate an event where the signal strengthfrom the source gNB decreases and the signal strength from the targetgNB increases at the UE; upon receipt of the measurement value, thesource gNB may recognize UE mobility and prepare for a handover.

That is, the source gNB prepares for the inter-gNB Type 2 handover atstep 3 g-20 and requests to the target eNB, at step 3 g-25, for addingan SeNB for dual connectivity via Xn signaling (inter-gNB controlsignaling, e.g., X2 signaling). The request message includes PDCPconfiguration information for a PDCP entity reserved per SCell to beadded (no PDCP configuration is performed in requesting for adding SeNBsin the legacy LTE) and split bearer configuration information for thehandover.

Upon receipt of the request message, the target gNB performs PDCPestablishment and establishes RLC and MAC entities for a split bearer atstep 3 g-30 and transmits an SeNB addition response (SeNB ADDITIONRESPONSE) message to the source gNB. The response message including thecontent of the received SeNB addition request message may beretransmitted at step 3 g-35.

Upon receipt of the SeNB addition response message, the source gNBtransmits an RRC Reconfiguration Request (rrcReconfigReg) message to theUE at step 3 g-40. This message may include SCG configurationinformation of the target gNB, SRB and DRB split bearer configurationinformation, and RRC diversity configuration information.

If the UE receives the RRC diversity configuration information, PDCPSDUs are sent to the RLC entities for the PCell and PSCell in the UEuntil the RRC diversity configuration is deactivated. The uplink RRCdiversity may be deactivated when the SRB is reconfigured from a splitbearer to an MCG bearer or an explicit deactivation instruction isreceived via an RRC message (e g , handover command message). At step 3g-45, the UE establishes S-MAC and S-RLC entities for the SeNB andreconfigures the MCG bearers, i.e., all SRBs and DRBs, into splitbearers according to the received RRC message.

Next, the UE performs a random access procedure to the target gNB atstep 3 g-50 and performs uplink transmission/downlink transmissionto/from source and target gNBs at steps 3 g-55, 3 g-60, 3 g-65, and 3g-70. The UE is capable of establishing connections to the source andtarget gNBs simultaneously to perform data communication without anytime interruption in Phase 1 as denoted by reference numbers 3 g-15 to 3g-70.

After Phase 1, if the measurement value of the UE indicates, at step 3g-75, an event triggering a handover to the target gNB, the source gNBmakes a handover determination (Phase 2) at step 3 g-80. The measurementvalue may indicate an event where the signal strength from the sourcegNB decreases and the signal strength from the target gNB increases atthe UE; it may be possible to reuse handover determinative LTE events oradd new events.

If the source gNB requests to the target gNB for a Type 2 handover viaXn signaling at step 3 g-85, the target gNB activates PDCP entities andlinks PDCP entities to corresponding RLC entities at step 3 g-90. Next,the target gNB transmits a Type 2 handover response to the source gNBvia Xn signaling at step 3 g-95, and the source gNB transmits receivedPDCP SDUs to the target gNB via Xn signaling at step 3 g-100.

The source eNB transmits a Type 2 handover command to the UE via an RRCmessage (RRCConnectionReconfiguration) at step 3 g-105. This RRC messageexplicitly or implicitly includes a configuration indicative ofswitching roles between the PCell and the PSCell belonging to the sourceand target gNBs.

The UE performs the Type 2 handover to the PSCell of the target gNB atstep 3 g-110 and transmits an RRC message, i.e., Type 2 handovercomplete message, through the PSCell of the source gNB and the PCell ofthe target gNB at step 3 g-115. During the Type 2 handover, the UEmaintains the old Layer 1 communication, cancels configuration of PHR inLayer 2 (MAC), and adjusts locations of PHs in the PHR according to thechange of the PCell and PSCell. In Layer 3, radio link monitoring (RLM)for determining radio link failure (RLF) is adjusted according to thechange of the PCell and PSCell. That is, as the PCell (Cell1) is changedto the PSCell, a secondary RLM (sRLM) configuration condition isactivated.

Likewise, the measurement value report is adjusted according to thechange of the PCell and the SCell, and the index (ServCellIndex) of theserving cell is adjusted. That is, the serving cell index of Cell1 (oldPCell) is changed from index 0 to index x, and the serving cell index ofCell3 (old PSCell) is changed from index y to index 0. The ServCellIndexof the old PCell may be configured according to one of the followingmethods.

-   -   Option 1: A SCellIndex is explicitly transmitted via the Type 2        handover command message at step 3 g-105 or the RRC connection        reconfiguration message at step 3 g-40.    -   Option 2: The SCellIndex used by the new PCell (Cell2) is        automatically allocated.

Next, the UE maintains uplink transmissions/downlink receptions to/fromthe source and target gNBs at steps 3 g-120, 3 g-125, 3 g-130, and 3g-135. The UE is capable of switching roles between the PCell of thesource gNB and the PSCell of the target gNB and establishing connectionssimultaneously to the two gNBs for data communication without any timerinterruption in Phase 2 as denoted by reference numbers 3 g-75 to 3g-135.

After Phase 2, if the measurement value of the UE indicates, at step 3g-140, an event indicative of releasing the connection to the sourcegNB, the target gNB determines to release the dual connectivityconfigured with the source gNB (Phase 3) at step 3 g-145. Themeasurement value may indicate an event where the signal strength fromthe source gNB is less than a predetermined threshold value at the UEand inappropriate for communication; it may be possible to reuse LTEevents or add new events.

The target gNB instructs the source gNB, at step 3 g-150, to release theSCG via Xn signaling and notifies the UE of the SCG release at step 3g-155 via an RRC message. Afterward, the UE and the target gNB maintainthe uplink/downlink communications at steps 3 g-160 and 3 g-165.

FIGS. 3HA and 3HB are schematic diagrams for explaining a DC- and RLCsplit bearer-based inter-gNB handover operation and a protocol structureaccording to embodiment 3-1 of the disclosure.

In Phase 0, a UE is connected to gNB 1 for basic data communication inthe NR system as denoted by reference number 3 h-05. In the disclosure,it is assumed that the gNB 1 hosts a PCell and an SCell for convenienceof explanation. In this phase, the gNB 1 configures an MCG bearer fordata communication only through a serving cell of an MeNB, and each PDCPentity is connected to one RLC, which is connected to a MAC entity via alogical channel as denoted by reference number 3 h-10. The UE configuresPDCP, RLC, and MAC according to the bearer configuration with the gNB 1and receives a control signal and data through the PCell (Cell1). The UEalso transmits HARQ feedback, scheduling requests, and CSI through thePCell (Cell1) and performs data communication through the SCell (Cell2).The SCell transitions between an activated state and a deactivated staterepeatedly under the control of the gNB 1 as denoted by reference number3 h-15.

If the gNB 1 makes a dual connectivity determination for a handover uponfulfilment of a predetermined condition, dual connectivity is configuredin Phase 1 as denoted by reference number 3 h-20. In this phase, thehandover is determined to be made to the target cell belonging to thegNB 1. Next, the source cell (MCG) of the gNB 1 establishes dualconnectivity with a target cell (SCG) including a PSCell (Cell3) as anadditional PUCCH serving cell and an SCell (Cell4) and reconfigures theold MCG bearer into a split bearer at steps 3 h-25 and 3 h-30. Thismeans that the source cell PDCP entities of the gNB 1 are split toestablish links to the RLC entities for the source and target cells. Inthis phase, PDCP reordering is not performed in the target cell becausethere is no need of any PDCP reordering operations for a handoverbetween the cells belonging to the same gNB.

As the dual connectivity is established, the UE establishes additionalRLC entities and resets a new MAC entity while maintaining the old PDCPreordering operations for SRB and DRB and RLC and MAC configurations forthe source cell as denoted by reference number 3 h-35.

If the gNB 1 detects an event triggering a handover from a measurementreport value of the UE, e.g., if a signal strength from the target cellis greater than the signal strength from the source cell over apredetermined threshold value, this leads to Phase 2 in which the rolesare switched between the PCell and the PSCell as denoted by referencenumber 3 h-40. In this phase, the roles are switched between the PCelland the PSCell with no change of the old bearer configuration, and theS1-U connection to the old gNB 1 is also maintained as denoted byreference numbers 3 h-45 and 3 h-50.

As in the gNB, in the UE the roles are switched between the PCell andthe PSCell while maintaining the old protocol configurations, whichleads to canceling of a previous configuration of a PHR and adjustinglocations of PHs in the PHR as denoted by reference number 3 h-55.

If the gNB 1 detects an event triggering dual connectivity release ofthe source cell from a measurement report value of the UE, e.g., if thesignal strength from the source cell becomes equal to or less than apredetermined threshold value, this leads to Phase 3 in which the dualconnectivity is released as denoted by reference number 3 h-60.

In this phase, the split bearer is reconfigured into an MCB bearer andthe bearer configuration for the source cell is released as denoted byreference number 3 h-65; an SCG release request signal is transmitted tothe UE. Likewise, the UE releases the RLC and MAC as denoted byreference number 3 h-70 and performs data communication with the newlyconfigured target cell.

FIGS. 1A and 3IB are signal flow diagrams illustrating a DC- and RLCsplit bearer-based handover procedure according to embodiment 3-2 of thedisclosure.

A description is made of the per-phase signal flows in the DC- and RLCsplit bearer-based inter-gNB handover procedure in detail with referenceto FIGS. 31A and 31B.

It is assumed that the UE 3 i-01 in the state of being connected to asource cell 3 i-03 of a source gNB 3 i-02 receives a downlink controlsignal (PDCCH) and data (PDSCH) at step 3 i-05 and transmits an uplinkcontrol signal (PUCCH) and data (PUSCH) at step 3 i-10 in Phase 0. Inthis phase, it may be possible to receive the downlink control signaland transmit the uplink control signal through the PCell of the sourcegNB and perform further data transmission/reception through an SCellunder the control of the gNB.

The UE measures neighboring cells periodically or as configured by thegNB and, if a predetermined condition is fulfilled, it transmits to thecorresponding source cell, at step 3 i-15, a measurement valueindicating the necessity of dual connectivity for a handover, whichleads to Phase 1. The measurement value may indicate an event where thesignal strength from the source cell decreases and the signal strengthfrom the target cell increases at the UE; upon receipt of themeasurement value, the source cell may recognize UE mobility and preparefor an intra-gNB handover.

That is, the source cell prepares for the intra-gNB Type 2 handover atstep 3 i-20 and establishes a split bearer for performing the handoverto the target cell. If a dual connectivity preparation step iscompleted, the source cell transmits an rrcReconfigReq message to the UEat step 3 i-25. This message may include CSG configuration informationof the target cell, SRB and DRB split bearer configuration information,and RRC diversity configuration information.

If the UE receives the RRC diversity configuration information, PDCPSDUs are sent to the RLC entities for the PCell and PSCell in the UEuntil the RRC diversity configuration is deactivated. The uplink RRCdiversity may be deactivated when the SRB is reconfigured from a splitbearer to an MCG bearer or an explicit deactivation instruction isreceived via an RRC message (e g , handover command message).

At step 3 i-30, the UE establishes S-MAC and S-RLC entities for the SCGand reconfigures the MCG bearers, i.e., all SRBs and DRBs, into splitbearers according to the received RRC message. Next, the UE performs arandom access procedure to the target gNB at step 3 i-35 and performsuplink transmission/downlink transmission to/from source and target gNBsat steps 3 i-40, 3 i-45, 3 i-50, and 3 i-55. The UE is capable ofestablishing connections to the source and target gNBs simultaneously toperform data communication without any time interruption in Phase 1 asdenoted by reference numbers 3 i-15 to 3 i-55.

After Phase 1, if the measurement value of the UE indicates, at step 3i-60, an event triggering a handover to the target cell, the source cellmakes an handover determination (Phase 2) at step 3 i-65. Themeasurement value may indicate an event where the signal strength fromthe source cell decreases and the signal strength from the target cellincreases at the UE; it may be possible to reuse handover determinativeLTE events or add new events.

If the source cell receives the above message, it performs an operationfor switching roles between the PCell and the PSCell. The source celltransmits a Type 2 handover command to the UE via an RRC message(RRCConnectionReconfiguration) at step 3 i-70. This RRC messageexplicitly or implicitly includes a configuration indicative ofswitching roles between the source cell and the PCell and the PSCellbelonging to the target gNB.

The UE performs the Type 2 handover to the PSCell of the target cell atstep 3 i-75 and transmits an RRC message, i.e., Type 2 handover completemessage, to the PSCell of the source cell and the PCell of the targetcell at step 3 i-80. During the Type 2 handover, the UE maintains theold Layer 1 communication, cancels a configuration of PHR in Layer 2(MAC), and adjusts locations of PHs in the PHR according to the changeof the PCell and PSCell. In Layer 3, radio link monitoring (RLM) fordetermining radio link failure (RLF) is adjusted according to the changeof the PCell and PSCell. That is, as the PCell (Cell1) is changed to thePSCell, a secondary RLM (sRLM) configuration condition is activated.

Likewise, the measurement value report is adjusted according to thechange of the PCell and the SCell, and the index (ServCellIndex) of theserving cell is adjusted. That is, the serving cell index of Cell1 (oldPCell) is changed from index 0 to index x, and the serving cell index ofCell3 (old PSCell) is changed from index y to index 0. The ServCellIndexof the old PCell may be configured according to one of the followingmethods.

-   -   Option 1: A SCellIndex is explicitly transmitted via the Type 2        handover command message at step 3 i-70 or the RRC connection        reconfiguration message at step 3 i-25.    -   Option 2: The SCellIndex used by the new PCell (Cell2) is        automatically allocated.

Next, the UE maintains uplink transmissions/downlink receptions to/fromthe source and target gNBs at steps 3 i-85, 3 i-90, 3 i-95, and 3 i-100.The UE is capable of switching roles between the PCell of the source gNBand the PSCell of the target gNB and establishing connectionssimultaneously to the two gNBs for data communication without any timerinterruption in Phase 2 as denoted by reference numbers 3 i-75 to 3i-135.

After Phase 2, if the measurement value of the UE indicates, at step 3i-105, an event indicative of releasing the source cell, the target celldetermines to release the dual connectivity configured with the sourcecell (Phase 3) at step 3 i-110. The measurement value may indicate anevent where the signal strength from the source gNB is less than apredetermined threshold value at the UE and inappropriate forcommunication; it may be possible to reuse LTE events or add new events.

The source gNB reconfigures the split bearer into an MCG bearer,releases the bearer configuration (MAC and RLC) for the source cell, andnotifies the UE of the SCG release via an RRC message at step 115.Afterward, the UE and the target cell maintain uplinktransmission/downlink reception at steps 3 i-120 and 3 i-125.

FIG. 3J is a flowchart illustrating a DC- and RLC split bearer-basedType 2 handover procedure of a UE according to an embodiment of thedisclosure.

If the UE in uplink/downlink data communication with a gNB through asource cell at step 3 j-01 (this state is referred to as Phase 0)detects a change in a measurement value at step 3 j-05 as it moves, itreports the measurement value indicative of a type of the event to agNB. The current state of the UE and the measurement determines asubsequent operation.

The disclosure proposes a DC- and RLC split bearer-based handover methodfor zeroing time interruption. If the UE operating in Phase 0 detects ameasurement value corresponding to Phase 1, it transmits the measurementvalue to a gNB at step 3 j-10.

The UE receives dual connectivity configuration information, at step 3j-15, from the gNB, which determines a necessity of dual connectivityand transmits the dual connectivity configuration information andconfigures a split bearer for dual connectivity at step 3 j-20. Thesplit bearer configuration is applied to all SRBs and DRBs, and the UEestablishes S-MAC and S-RLC entities according to an SCG configuration(SCG-Config). Next, the UE performs dual connectivity uplink/downlinkdata communication at step 3 j-25.

While operating in Phase 1, if the UE detects an event indicative of anecessity of a handover to a target cell, i.e., an event triggeringPhase 2, at step 3 j-05, it transmits the measurement value indicativeof a type of the event to the gNB at step 3 j-10.

Next, the UE receives, at step 3 j-30, an RRC message instructing a Type2 handover to a target cell from the gNB and changes the roles andconfigurations of the PCell and PSCell at step 3 j-35. During the Type 2handover, the UE maintains the old Layer 1 communication, cancels an oldconfiguration of PHR in Layer 2 (MAC), and adjusts locations of PHs inthe PHR according to the change of the PCell and PSCell. In Layer 3, theRLM for determining RLF is adjusted according to the change of the PCelland PSCell. That is, as the PCell (Cell1) is changed to the PSCell, ansRLM configuration condition is activated.

Likewise, the measurement value report is adjusted according to thechange of the PCell and PSCell, and the ServCellIndex is adjusted too.After switching the roles between the PCell and PSCell, the UE performsdual connectivity uplink/downlink data communication at step 3 j-40.

While operating in Phase 1, if the UE detects an event indicative of anecessity of releasing the source cell, i.e., an event triggering Phase3, at step 3 j-05, it transmits the measurement value indicative of atype of the event to the gNB at step 3 j-10.

Next, the UE receives, at step 3 j-45, an RRC message instructingrelease of the SCG bearer of the source cell from the gNB and releasesthe SCG bearer-related MAC and RLC at step 3 j-50. Afterward, the UEperforms uplink/downlink data communication through the target cell atstep 3 j-55.

The UE operation varies according to the cell to which the UE belongs.In the disclosure, the descriptions are made of the Type 2 handoverprocedures in association with 4 cells with reference to FIGS. 3FA, 3FB,3HA, and 3HB. Tables 2a and 2b summarize operations of a UE before andafter receiving a Type 2 handover command It is preferable to understandthat the contents of Tables 2a and 2b are associated with each other.

TABLE 2a Cell 1 Cell 3 Cell 2, 4 Before receipt of PCell PSCell SCellType 2 handover command After receipt of PSCell PCell SCell Type 2handover command Layer 1 (Cell UE continues UE continues UE continuesgroup) performing current performing current performing currentoperation in this operation in this operation in this cell: i.e., cell:i.e., cell: i.e., PUCCH/PUSCH tx PUCCH/PUSCH tx PUSCH tx (if PDCCH/PDSCHrx PDCCH/PDSCH rx uplink is configured) PDCCH/PDSCH rx

TABLE 2b Layer 2 Cancel triggered Cancel triggered Continue (MAC) PHRand change PHR and change performing locations of PHs in locations ofPHs in current PHR (move Type 2 PHR (move Type 2 operation PH from firstoctet PH from third octet to third octet and to first octet and Type 1PH from Type 1 PH from second octet to fourth octet to fourth octet insecond octet in PHR MAC CE. For PHR MAC CE. For reference, 0^(th) octetreference, 0^(th) octet indicates SCell indicates SCell index of MAC CE)index of MAC CE) Layer 3 Continue RLM Continue RLM Continue (RRC)operation using operation using performing parameter for parameter forcurrent sRLM (if RLF is sRLM (if RLF is operation detected, triggerdetected, trigger sRLF-related sRLF-related operations). Stopoperations). Start monitoring for monitoring for paging. Start paging.Start considering considering measurement result measurement result ofthis serving cell of this serving cell as measurement as measurementresult of PSCell. result of PCell. Update Update ServCellIndexServCellIndex from 0 to x*. from y to 0**.

In the above Layer 3 operation, ServCellIndex of the old PCell isconfigured according to one of the two methods as follows.

-   -   Option 1: The SCellIndex is explicitly transmitted via a Type 2        handover command or RRC connection reconfiguration.    -   Option 2: The SCelIndex used in the new PCell (Cell2) is        automatically assigned.

The bearer management method is changed according to the change of Phasein the UE. In the disclosure, an MCG bearer and a split bearer areconfigured according to Phase because a dual connectivity-based handoveris performed. Table 3 summarizes SRB, DRB, and MAC management accordingto Phase transition.

TABLE 3 Phase 0→Phase 1 Phase 1→Phase 2 Phase 2→Phase 3 DC is configuredType 2 handover DC is released SRB PDCP Continue PDCP Continue PDCPContinue PDCP reordering reordering reordering operation. operation.operation. Trigger PDCP status report. RLC Configure Maintain RLC AMaintain RLC B additional RLC and RLC B and release RLC (RLC B)continuously. A. Maintain RLC (RLC A) continuously. DRB PDCP Identicalwith SRB Identical with SRB Identical with SRB RLC Identical with SRBIdentical with SRB Identical with SRB MAC Maintain MAC A ReconfigureMaintain MAC B continuously. MAC A** Release MAC A Reset new MACReconfigure (MAC B) MAC B**

Here, it is assumed that the PDCP reordering operation is alwayspossible for the SRB and that the MAC reconfiguration follows the MACconfiguration in Table 2.

The above UE operation is applicable to the inter-gNB and inter-gNB Type2 handovers in the same manner, and the UE characteristics may besummarized in comparison with the Type 1 handover in the disclosure.Table 4 summarizes the legacy LTE Type 1 handover and the DC- and RLCsplit bearer-based Type 2 handover proposed in the disclosure in amanner of a comparison.

TABLE 4 Type 1 HO Type HO Radio interface- No Add secondary cell groupbased pre-phase (SCG) Radio interface- No Release secondary cell groupbase post-phase (SCG) RRC message Type 1 handover command Type 2handover command triggering e.g., e.g., rcConnectionReconfigurationrrcConnectionReconfiguration (target cell ID, target indicating Type 2handover frequency, C-RNTI) including mobilityControlInfo Target cellIncluded in Included in identifier and mobilityControlInfo of HOmobilityControlInfo SCG absolute radio- command message included in SCGaddition frequency channel message in previous phase number (ARFCN) oftarget frequency L1 Stop L1 operation using Maintain L1 operation usingsource source and target Start L1 operation using target SCellDeactivate SCell upon Type Maintain SCell status upon 1 HO command Type2 HO command

FIG. 3k is a block diagram illustrating a configuration of a UEaccording to an embodiment of the disclosure.

In reference to FIG. 3K, the UE includes a radio frequency (RF)processing unit 3 k-10, a baseband processing unit 3 k-20, a memory 3k-30, and a controller 3 k-40.

The RF processing unit 3 k-10 takes charge of signal band conversion andamplification for transmitting signals over a radio channel That is, theRF processing unit 3 k-10 up-converts a baseband signal output from thebaseband processing unit 3 k-20 to an RF band signal for transmissionthrough antennas and down-converts an RF band signal received throughthe antenna to a baseband signal.

For example, the RF processing unit 3 k-10 may include a transmissionfilter, a reception filter, an amplifier, a mixer, an oscillator, adigital-to-analog converter (DAC), and an analog-to-digital convertor(ADC). Although one antenna is depicted in the drawing, the terminal mayinclude a plurality of antennas. The RF processing unit 3 k-10 mayinclude a plurality of RF chains. The RF processing unit 3 k-10 mayperform beamforming For beamforming, the RF processing unit 3 k-10 mayadjust the phases and sizes of the signal transmitted/received throughthe antennas or antenna elements. The RF processing unit 3 k-10 mayperform a MIMO operation to receive a signal on multiple layers.

The baseband processing unit 3 k-20 takes charge of conversion betweenbaseband signals and bit strings according to a physical layer protocolof the system. For example, the baseband processing unit 3 k-20 performsencoding and modulation on the transmit bit strings to generate complexsymbols in data transmission mode. The baseband processing unit 3 k-20also performs demodulation and decoding on the baseband signal from theRF processing unit 3 k-10 to recover the received bit strings in datareception mode.

For the case of an orthogonal frequency division multiplexing (OFDM)system, the baseband processing unit 3 k-20 performs encoding andmodulation on the transmit bit strings to generate complex symbols, mapsthe complex symbols to subcarriers, performs inverse fast Fouriertransform (IFFT) on the subcarriers, and inserts a cyclic prefix (CP) togenerate OFDM symbols in the data transmission mode. The basebandprocessing unit 3 k-20 splits the baseband signal from the RF processingunit 3 k-10 into OFDM symbols, recovers the signals mapped to thesubcarriers through fast Fourier transform (FFT), and performsdemodulation and decoding to recover the bit strings in the datareception mode.

The baseband processing unit 3 k-20 and the RF processing unit 3 k-10take charge of transmitting and receiving signals as described above.Accordingly, the baseband processing unit 3 k-20 and the RF processingunit 3 k-10 may be referred to as a transmission unit, a reception unit,a transceiver, or a communication unit. At least one of the basebandprocessing unit 3 k-20 and the RF processing unit 3 k-10 may include aplurality of communication modules for supporting different radio accesstechnologies. At least one of the baseband processing unit 3 k-20 andthe RF processing unit 3 k-10 may include a plurality of communicationmodules for processing different frequency bands signals. Examples ofthe radio access technologies include WLAN (e.g., IEEE 802.11) andcellular network (e.g., LTE). Examples of the different frequency bandsmay include super high frequency (SHF) band (e.g., 2.5 GHz and 5 GHz)and millimeter wave (mmWave) bands (e.g., 60 GHz).

The memory 3 k-30 stores basic programs for operation of the terminal,application programs, and data such as configuration information. Inparticular, the memory 3 k-30 may store information related to a secondaccess node that performs radio communication using a second radioaccess technology. The memory 3 k-30 provides the stored data inresponse to a request from the controller 3 k-40.

The controller 3 k-40 controls overall operations of the terminal. Forexample, the controller 3 k-40 controls the baseband processing unit 3k-20 and the RF processing unit 3 k-10 to transmit/receive signals. Thecontroller 3 k-40 also writes and reads data to and from the memory 3k-30. In order to accomplish this, the controller 3 k-40 may include atleast one processor. For example, the controller 3 k-40 may include acommunication processor (CP) for controlling communication and anapplication processor (AP) for providing higher layer processing, e.g.,application layer protocol processing.

FIG. 3L is a block diagram illustrating a configuration of an NR gNBaccording to an embodiment of the disclosure.

As shown in the drawing, the NR gNB includes an RF processing unit 3l-10, a baseband processing unit 3 l-20, a backhaul communication unit 3l-30, a memory 3 l-40, and a controller 3 l-50.

The RF processing unit 3 l-10 takes charge of signal band conversion andamplification for transmitting signals over a radio channel. That is,the RF processing unit 3 l-10 up-converts a baseband signal output fromthe baseband processing unit 3 l-20 to an RF band signal fortransmission through antennas and down-converts an RF band signalreceived through the antennas to a baseband signal.

For example, the RF processing unit 3 l-10 may include a transmissionfilter, a reception filter, an amplifier, a mixer, an oscillator, a DAC,and an ADC. Although one antenna is depicted in FIG. 31, the NR gNB mayinclude a plurality of antennas. The RF processing unit 3 l-10 mayinclude a plurality of RF chains. The RF processing unit 3 l-10 mayperform beamforming For beamforming, the RF processing unit 3 l-10 mayadjust the phases and sizes of the signal transmitted/received throughthe antennas or antenna elements. The RF processing unit 3 l-10 mayperform a downlink MIMO operation to transmit a signal on multiplelayers.

The baseband processing unit 3 l-20 takes charge of converting betweenbaseband signals and bit strings according to a physical layer protocolof a first radio access technology. For example, the baseband processingunit 3 l-20 performs encoding and modulation on the transmit bit stringsto generate complex symbols in data transmission mode. The basebandprocessing unit 3 l-20 also performs demodulation and decoding onbaseband signals from the RF processing unit 3 l-10 to recover thereceived bit strings in data reception mode.

For the case of an OFDM system, the baseband processing unit 3 l-20performs encoding and modulation on the transmit bit string to generatecomplex symbols, maps the complex symbols to subcarriers, performs IFFTon the subcarriers, and inserts a CP to generate OFDM symbols in thedata transmission mode. The baseband processing unit 3 l-20 splitsbaseband signals from the RF processing unit 3 l-10 into OFDM symbols,recovers the signals mapped to the subcarriers through FFT, and performsdemodulation and decoding to recover the bit strings in the datareception mode. The baseband processing unit 3 l-20 and the RFprocessing unit 3 l-10 take charge of transmitting and receiving signalsas described above. Accordingly, the baseband processing unit 3 l-20 andthe RF processing unit 3 l-10 may be referred to as a transmission unit,a reception unit, a transceiver, or a communication unit.

The backhaul communication unit 3 l-30 provides an interface forcommunication with other network nodes. That is, the backhaulcommunication unit 3 l-30 converts a bit string transmitted from an NRgNB to another node, e.g., secondary base station and core network, to aphysical signal and converts a physical signal received from anothernode to a bit string.

The memory 3 l-40 stores basic programs for operation of the NR gNB,application programs, and data such as configuration information. Inparticular, the memory 3 l-40 may store the information on the bearersallocated to the connected terminal and a measurement result reported bythe terminal. The memory 3 l-40 may also store the information ascriteria for determining whether to enable or disable multi-connectivityfor the terminal. The memory 3 l-40 provides the stored data in responseto a request from the controller 3 l-50.

The controller 3 l-50 may control overall operations of the NR gNB. Forexample, the controller 3 l-50 controls the baseband processing unit 3l-20, the RF processing unit 3 l-10, and the backhaul communication unit3 l-30 for transmitting/receiving signals. The controller 3 l-50 alsowrites and reads data to and from the memory 3 l-40. In order toaccomplish this, the controller 3 l-50 may include at least oneprocessor.

An embodiment of the disclosure may include the followingcharacteristics.

1. Characteristics of UE performing Type 2 handover

-   -   Method for handover to a serving cell satisfying a predetermined        condition among preconfigured serving cells.    -   A method for configuring a bearer differently according to        handover phase    -   Configure split bearers for all SRBs and DRBs except for SRB 0        and provide target cell information, target frequency        information, random access parameter information, etc. in        preparation phase    -   UE operation in Type 2 HO execution phase (method for changing        roles between PCell and PSCell)    -   Change locations of PCell and PSCell in PHR in UE MAC operation    -   Change parameter for RLM in UE RRC operation    -   Update serving cell index value for measurement report in UE RRC        operation    -   Method for performing data recovery in wrap-up phase

2. Difference between Type 2 handover and Type 1 handover

-   -   Presence/Absence of pre-step (adding SCG) before handover    -   Presence/Absence of post-step (releasing SCG) after handover    -   Method for commanding Type 2 handover via RRC connection        reconfiguration    -   Method for transmitting target cell ID and frequency information        via SCG addition message    -   Method for performing L 1 transmission continuously through        source and target cells    -   Method for maintaining S Cell status continuously when receiving        Type 2 handover command

3. RRC diversity execution and stop operation in Type 2 handover

-   -   Method for deactivating RRC diversity when split bearer is        reconfigured into MCG bearer

Method for deactivating RRC diversity when being explicitly indicatedvia RRC message (e.g., handover command message.

In the embodiments of the disclosure, the components are described insingular or plural forms depending on the embodiment. However, thesingular and plural forms are selected appropriately for the proposedsituation just for explanatory convenience without any intention oflimiting the disclosure thereto; thus, the singular form includes theplural forms as well, unless the context clearly indicates otherwise.

Although the description has been made with reference to particularembodiments, the disclosure can be implemented with variousmodifications without departing from the scope of the present invention.Thus, the disclosure is not limited to the particular embodimentsdisclosed, and it will include the following claims and theirequivalents.

1. A method of a first base station in a wireless communication system,the method comprising: transmitting, to a second base station, anaddition request message for requesting an addition of the second basestation, in a case that a handover for a terminal served by the firstbase station is determined; transmitting, to the second base station, ahandover request message including information for changing a PrimaryCell (PCell) of the first base station to a Primary Secondary Cell(PSCell) and the PSCell of the second base station to the PCell for theterminal based on a predetermined condition being satisfied; andreleasing a connection between the first base station and the terminal,based on receiving a release request message from the second basestation.
 2. The method of claim 1, wherein the addition request messagecomprises configuration information associated with a split bearerbetween the first and the second base station, and wherein the splitbearer-comprises a first split bearer connecting a first packet dataconvergence protocol (PDCP) included in the first base station to asecond radio link control (RLC) included in the second base station anda second split bearer connecting a second PDCP included in the secondbase station to a first RLC included in the first base station.
 3. Themethod of claim 2, wherein the configuration information associated withthe split bearer comprises configuration information on the second RLCassociated with the first and second split bearers, and configurationinformation on the second PDCP associated with the second split bearer,and wherein the second PDCP is established by the second base stationbased on the configuration information on the second PDCP and maintainedin a deactivated state.
 4. The method of claim 2, further comprising:transmitting, to the terminal, a radio resource control (RRC)reconfiguration message including configuration information associatedwith the first split bearer, based on receiving an addition responsemessage in response to the addition request message; receiving, from thesecond base station, a handover request acknowledgement message, inresponse to the handover request message after transmitting the RRCreconfiguration message; and transmitting, to the terminal, a handovercommand message including information indicating changes from the PCellof the first base station to the PSCell and from the PSCell of thesecond base station to the PCell, based on the handover requestacknowledgement message.
 5. The method of claim 4, further comprisingdeactivating the first PDCP based on the handover requestacknowledgement message.
 6. A method of a terminal in a wirelesscommunication system, the method comprising: receiving, from a firstbase station, a radio resource control (RRC) reconfiguration messageincluding configuration information associated with a split bearerbetween the first base station and a second base station added to theterminal by the first base station; receiving, from the first basestation, a handover command message including information indicatingchanges from a Primary Cell (PCell) of the first base station to aPrimary Secondary Cell (PSCell) and from the PSCell of the second basestation to the PCell; and releasing a wireless connection to the firstbase station.
 7. The method of claim 6, wherein the split bearer betweenthe first and second base stations comprises a first split bearerconnecting a first packet data convergence protocol (PDCP) included inthe first base station to a second radio link control (RLC) included inthe second base station and a second split bearer connecting a secondPDCP included in the second base station to a first RLC included in thefirst base station, and wherein the second PDCP is established based onthe configuration information on the second PDCP, which is included inan addition request message for adding the second base station, andmaintained in a deactivated state.
 8. The method of claim 7, furthercomprising configuring all bearers for the first base station as thefirst split bearer based on the RRC reconfiguration message.
 9. A firstbase station in a wireless communication system, the first base stationcomprising: a transceiver configured to transmit an addition requestmessage for requesting an addition of the second base station, in a casethat a handover for a terminal served by the first base station isdetermined; and a controller configured to: control the transceiver totransmit, to the second base station, a handover request messageincluding information for changing a Primary Cell (PCell) of the firstbase station to a Primary Secondary Cell (PSCell) and the PSCell of thesecond base station to the PCell for the terminal based on apredetermined condition being satisfied, and release a connectionbetween the first base station and the terminal based on receiving arelease request message from the second base station.
 10. The first basestation of claim 9, wherein the addition request message comprisesconfiguration information associated with a split bearer between thefirst and the second base station, and wherein the split bearercomprises a first split bearer connecting a first packet dataconvergence protocol (PDCP) included in the first base station to asecond radio link control (RLC) included in the second base station anda second split bearer connecting a second PDCP included in the secondbase station to a first RLC included in the first base station.
 11. Thefirst base station of claim 10, wherein the configuration informationassociated with the split bearer comprises configuration information onthe second RLC associated with the first and second split bearers andconfiguration information on the second PDCP associated with the secondsplit bearer, and wherein the second PDCP is established by the secondbase station based on the configuration information on the second PDCPand maintained in a deactivated state.
 12. The first base station ofclaim 10, wherein the controller is further configured to: control thetransceiver to transmit, to the terminal, a radio resource control (RRC)reconfiguration message including configuration information associatedwith the first split bearer, based on receiving an addition responsemessage in response to the addition request message, control thetransceiver to receive, from the second base station, a handover requestacknowledgement message in response to the handover request messageafter transmitting the RRC reconfiguration message, and control thetransceiver to transmit, to the terminal, a handover command messageincluding information indicating changes from the PCell of the firstbase station to the PSCell and from the PSCell of the second basestation to the PCell, based on the handover request acknowledgementmessage.
 13. A terminal in a wireless communication system, the terminalcomprising: a transceiver configured to receive, from a first basestation, a radio resource control (RRC) reconfiguration messageincluding configuration information associated with a split bearerbetween the first base station and a second base station added to theterminal by the first base station; and a controller configured to:control the transceiver to receive, from the first base station, ahandover command message including information indicating changes from aPrimary Cell (PCell) of the first base station to a Primary SecondaryCell (PS Cell) and from the PSCell of the second base station to thePCell, and release a wireless connection to the first base station. 14.The terminal of claim 13, wherein the split bearer between the first andsecond base stations comprises a first split bearer connecting a firstpacket data convergence protocol (PDCP) included in the first basestation to a second radio link control (RLC) included in the second basestation and a second split bearer connecting a second PDCP included inthe second base station to a first RLC included in the first basestation, and wherein the second PDCP is established based on theconfiguration information on the second PDCP, which is included in anaddition request message for adding the second base station, andmaintained in a deactivated state.
 15. The terminal of claim 14, whereinthe controller is further configured to control to configure all bearersfor the first base station as the first split bearer based on the RRCreconfiguration message.